Learning how to fix computer errors can be a real life saver at times. With the popularity of the personal computer rising everyday obtaining some basic technical computer repair skills can be very beneficial. When you first buy your computer it runs extremely smooth but as time goes on and your usage of your computer increases you may begin to notice a change its overall performance.

The power of present day computers is amazing, although they do have their problems and if you don’t know how to fix computer errors when they present themselves you can become very inconvenienced. Computers do require regular maintenance and they need to be periodically upgraded and if you fail to keep up with some easy maintenance you will no doubt experience problems. There are a few simple tasks that can be performed to fix computer errors and help prevent them from occurring in the future.

Tips That Will Help You Fix Computer Errors

If your computers registry becomes corrupt or unstable it will dramatically affect your computers performance in a very negative way. You may notice your computer is running extremely slow and your having to wait for programs to open or it takes awhile to switch from web page to web page. If you use your computer for work or school or maybe just to run the family’s budget, learning to fix computer problems can be extremely beneficial.

When your computers registry has been corrupted you may have error messages popping up on your screen such as “fatal .exe error” or “.dll file error” and these type of errors can cause your system to shut down or freeze up leaving you with a computer that you cannot use. When these type of errors occur it can be extremely frustrating because you may be in the middle of some important work so if your learn how to fix computer errors such as these you can avoid serious down time.

One of the first steps you should take in efforts to solve your problem would be to run your disk defragmenter. Running the disk defragmenter may reduce the occurrence of errors by condensing all the files in need of repair.

To fix computer errors that are related to your computers registry, you should complete a registry scan so that all the unused, old and unwanted data can be detected and removed. To clean your computers registry you will need to buy a good registry cleaner program. I want to emphasize on the word “Buy” because there are a lot of free registry cleaners available but it’s a terrible idea to even try a free registry cleaner. Free registry cleaners will not only just not fix computer errors they will cause damage to your system. When it comes to the free registry cleaners the programmers will put in malicious code and adware and spyware programs that will collect and transmit your personal information and in many cases end up leaving your computer so damaged that it cannot be repaired.

Reg Clean is one of the more advanced registry cleaner programs available as it can perform a variety of preventative maintenance tasks as well as removing malicious spyware and viruses that have infected your registry. When you run a scan with Reg Clean it can fix computer errors as it cleans up your entire registry and it performs a registry backup while it is defragging your system.

There are a number of viruses out there that can really attack your system causing all sorts of problems. Spyware and virus programs can be the cause of a variety of computer errors. They are capable of overwriting program files or deleting necessary file extensions disabling important programs and limiting the functionality of your system. To fix computer errors that are a result of spyware and some viruses you can use updated antispyware and antivirus protection.

Damaged or corrupt programs or virus infections can cause serious damage to your computers boot section, and this will prevent your system from booting up properly or possibly not at all. When you need to fix computer errors related to your system booting up properly you should use your Windows XP Boot CD as this can repair the Windows XP installation which can overwrite computer errors picked up through spyware or viruses.

If the problems that you are having are directly related to your computers memory you will experience some of the following problems; system crashes, system hang or computer freeze, blue screen, constant restarts and crashing software programs. To fix computer errors related to your systems memory there are specific software programs that can help free up some memory space which will help solve RAM related problems. Improving your systems memory which is also known as RAM (random access memory), will improve your computers performance dramatically so I would highly advice you to do a computer memory test. To complete a memory test there is specific software available for such a task, one program that I am aware of that is very effective is called Memtest86, this can help you zero in on your problem allowing you to fix computer errors brought to your attention.

If you have tried all the advice given in this article and your still experiencing computer problems I would do a search on the Internet for information on how to fix computer errors. You will find many websites that focus on computer basics and troubleshooting. I would be very careful though and really check the websites credentials so you can be sure that your getting advice from a reliable source. There is also a software program available that can help you learn how to fix computer errors but again I would be very cautious about any program that needs to be down loaded and run on your computer. Remember preventative maintenance can save you from a lot of unnecessary problems and one of the best preventative measures you can take is to purchase a reputable registry cleaner program and use it periodically.

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To start the most significant fact that should be stated is that the computer is a tool, and as with any educational tool, from books to crayons, it can be used to enhance the curriculum and promote learning, but it can also be misused and abused. In this essay, I will discuss the disadvantages of having computers in the classrooms due to the misuse and the abuse of this tool.

I found it hard to find research that had been done on this topic because not only is the research on the effectiveness of computers in the classroom scarce but the research that is there is often done by software companies and therefore may be biased. (Emmans 2001). Even though there is no clear-cut answer to the question of a computer being a friend or foe in the classroom, having an unsolvable question of good or bad brings many issues to light. For example, the fact that much of the software designed for children is appealing to them. If nothing else, it at least holds the children’s attention. Though this may seem like a positive characteristic, consider this, just because a television show holds your attention, does it necessarily educate you? The answer to this is simple, maybe some do, but certainly not all do, mostly they are just simply entertaining. This causes me to raise an eyebrow at some, not all, software. As a teacher, one must not use time-fillers, cause a child can watch television or play on a computer at home, but as a teacher, we must educate, and if there is no educational value in the software, what good is it for a teacher? On the defense for teachers, another reason for computers being a shortcoming is that sometimes the software is not obvious that it is non-educational. This can be a common mistake of any educator, being fooled that a product could be educational when it is merely entertainment software dressed up in an educational costume aimed at these gullible teachers.

According to Cindy C. Emmans (2001), a professor of Educational Technology at Central Washington University, on software in the classroom…

” Often feedback is the key to learning, and computers are appealing because this feedback can be immediate, which is of course a very effective learning tool. Unfortunately, this feedback is not often as effective as it might be, perhaps because it is not easy to return to the original question to try again, or the student must begin at the beginning to review the original content rather then backing up a step or two. In some cases, the feedback for the wrong answers is more appealing than that for the right answer, causing students to try and get the wrong answer simply for the entertainment value”.

Gerald W. Bracey sums it up adequately in a journal article called Principal by basically saying that the bells and whistles are all there, but the education is not, because it was not produced by someone who understands how children learn. (1996, p.6).

More arguments in the research area continued in September of 2000, the Alliance for Childhood published a statement against the use of computers in schools. More than 85 experts in various fields including psychiatry, education, and philosophy signed the statement in which calls for a suspension on the promoting introduction of computers into the nation’s elementary schools until there is a more careful assessment of their effect (Hafner, 2000). Another influence in opposition to computers in classrooms is that of Jane Healy, an educational psychologist and the author of “Failure to Connect,” a book criticizing educational applications of computers. Thomas Crampton interviewed Mrs. Healy and she declared that computers “can hurt children’s personal skills, work habits concentration, motivation, (and) the development of social skills” (IHT, October 2000, p. 19).

Another reason that computers in the classroom would prove to be a disadvantage is the availability of computers in the classroom to each individual student. It is rare to find a school that, in each classroom, has a computer supplied for each student. This then brings up the problem of scheduling and rotating the students to the computers available. (Tiene 2001) This begins a whole new ball game in which you are now consuming a lot of time in which could be used for more productive measures rather then scheduling computer time for each student. If this is the case, and only a specific amount of students can be on the computer at one time, then you are dividing your classroom, and not integrating it, as it should be. This causes many difficulties in teaching a whole group instruction, which leads to problems in skill development, since the attention of some students is lacking. (Tiene 2001).
On the Colorado state education web site (2003), I was able to find questions that were asked to teachers regarding computers in their classrooms. The teachers were asked, “What do you find unattractive about teaching in a computer based classroom?” The one teacher commented that, ” Students have a tendency to come in a print out their papers at the beginning of class instead of coming into class with a hard copy…” Another teacher said, ” Technological difficulty, your whole lesson could be shot for the day if the computer would go down”. When the teachers were asked about the difficulties they faced themselves and with the students due to computers in the classroom, they answered, ” It is hard to get the students attention when they are on the computers.” Another teacher commented, ” There are times that I send them to work and instead they are interacting with each other.” Another teacher stated her fear of the computer classroom by saying that, ” Students are at their own screens, they’re in their own little world, and they are not talking to their classmates, sometimes I think that they don’t even know half the names of all the people in their class.” (Barnes 2003) I feel that these teachers comments are very important when looking at the issue of computers in the classrooms, because these are the people that actually interact with the children in the classroom, they are not just some random research study by a software company, these people are the real thing, and they see how computers are effecting their classrooms.

Another issue of computers in the classrooms regards the child’s health. If a child were to be functioning on a computer for a long interlude of time or with incorrect positioning they will inadvertently obstruct their own health, some problems caused from this include muscular-skeletal injuries and vision problems. (MacArthur & Shneiderman, 1986).

Another issue concerning computer use in classrooms is that a lot of teachers have not been trained to use a computer, and many do not know how. An enormous amount of time would have to be consumed for the teachers to learn both the hardware and the software of the computer. They also would need time to collaborate with other teachers. Time is something that many teachers spend planning lessons and the weekly events of their classroom. The other problem that was just mentioned was the training of the teachers. Some educators do not have local training options available to them. Some do not have the time or money to spend on it. Another issue is that even if a teacher does go through training, there are always unsuspected things that can go wrong with a computer. If a teacher were to base their whole lesson on a computer, and it were to crash, and the teacher just being minimally skilled in using computers, would not be able to fix the system so that they could continue their lesson. (Tiene 2001).Therefore an on-site technology expert would be needed on site at all times in case any of these incidences would happen, and quite frankly I do not think that there are too many school districts looking for another expense.
Another reason for computers being a disadvantage in the classroom is that if the computer is Internet accessible, if this is the case, then the children can be exposed to Internet content that is not appropriate for their age level. They can also be exposed to child predators, which is a huge concern in today’s world.
Though this may seem far-fetched it truly is not in an article published on the gurdian angel websitein 2000 states,
“The facts are plain. Children are being targeted, solicited, and made victims by pedophiles. What do the ratios or statistics matter? Isn’t even one too many? These predators range from the simple minded closet pedophile who has surfaced because they believe they are safely anonymous behind their account alias, to the highly organized and skilled child pornography rings that operate predominantly off of US soil, behind quick discard web sites, and anonymous re-mailers, pushing their hideous wares for big profits. Have you ever heard of a child being molested or kidnapped in your hometown? Don’t you teach your kids to watch for certain things and, not to talk to, or go anywhere with, strangers for just that reason? This is our point. Just as there are real world lessons that you teach your children, there is a necessity to teach them cyber-world lessons. ” (Hook, 2000).
To put this quite simply, are you sure that your child is being watched very closely when accessing the Internet at school? It sure would be hard for one teacher to keep a close eye on each individual student in the classroom when they are all accessing the Internet at the same time. Therefore are you, as a parent or a teacher, really quite sure that a computer is necessary to learn in school? I mean, didn’t you, the parent or teacher, learn in school without the computer? I agree that learning the latest technology is a necessity, but I do not agree with using computers for classes like mathematics or reading.
To sum it all up, Computers in the classroom lacks research of it being an advantage in the classroom. Computers in the classroom may not provide the students with the proper education that they need if the software being used is not adequate. Computers may not be, depending on the school, made available to each student. The attention of the students is harder to get when they are on the computer. An inexperienced teacher in the technology area may cause many problems in the classroom, and consume valuable time that could be used to educate. Most schools do not provide an on site technician in case a difficulty may arise. The children’s health may be affected by long-term use of the computers, and probably the most frightening one is that these children can be exposed to child predators and unfiltered inappropriate content through the web while they are in school and in their classrooms presumed to be receiving their education.

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“Sketchpad, A Man-Machine Graphical Communication System”, described as one of the most influential computer programs ever written. This work was seminal in Human-Computer Interaction, Graphics and Graphical User Interfaces (GUIs), Computer Aided Design (CAD), and contraint/object-oriented programming. While watching this video, remember that the TX-2 computer (built circa 1958) on which the software ran was built from discrete transistors (not integrated circuits -it was room-sized) …

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Katie Criss is a graduate with a dual degree in Early Childhood Elementary Education, who enjoys writing and wants it to be seen! Also enjoys doing research and saving money!See this Authors Research by clicking here

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Fujitsu desktop computers are a great alternative to the more well-known desktop brands. There are several unique features that make the Fujitsu desktop computers stand out from other desktop computers. If you are looking for a computer that has a lot of versatility and many other great features then the Fujitsu may be right for you. The Fujitsu computer is similarly priced to other computer models, but since it contains many features and benefits Fujitsu computers stand out as a clear choice.

Fujitsu computers come with a large amount of processing power. Most of them have an Intel Core Duo processing unit, which makes the processing power of the computers faster than any computer that just has a single processing unit. Duo processing means processes take half as long. The processing unit of the Fujitsu is also environmentally friendly.

The processing unit is not the only part of Fujitsu desktop computers that are environmentally friendly. All Fujitsu computers comply with the European Union’s Restriction of Hazardous Substances procedures. Fujitsu also chooses products and materials that are safer for human use as well. This makes Fujitsu computers some of the most environmentally sound among the many brands any available in the market today.

Another great feature of Fujitsu computers is their ability to expand with additional hardware options. Fujitsu computers come with multiple PCI and PCI express slots which make it easy to install extra memory, network options, and other hardware needs. The multiple expansion slots make Fujitsu one of the most easily modified computers. Modification capabilities are becoming rarer these days, so a computer that still offers customization is a major plus.

Another great feature of Fujitsu computers is the graphics capabilities. With many computers the graphics card that comes with the computer is too small to run many games or programs. The graphics card that comes with a Fujitsu computer is capable of running almost any game out in the market today. Fujitsu computers also come fully equipped with the Windows Vista operating system.

A Fujitsu computer also comes with many external card reader slots and USB ports. The inclusion of so many different types of card readers makes it easy for anyone to upload their pictures or other information onto the Fujitsu computer. Fujitsu computers come with a card reader that is compatible with almost any memory device out there.

The last great benefit of a Fujitsu computer is the design of the CPU. The computer is designed to be taken apart and put back together quite easily. This makes it easy not only for users to upgrade the computer, but it also means that when the computer has to be taken in for repairs that they are able to be completed quickly and efficiently. The use of the easy-access CPU style is one of the biggest things that stick out about Fujitsu computers.

If you have never considered purchasing a Fujitsu computer, then consider looking into it for your next computer purchase. With all the features and benefits offered by Fujitsu, you will not be disappointed.

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In 1983, Fred Cohen coined the term “computer virus”, postulating a virus was "a program that can ‘infect’ other programs by modifying them to include a possibly evolved copy of itself.” The term virus is actually an acronym for Vital Information Resources Under Seize. Mr. Cohen expanded his definition a year later in his 1984 paper, “A Computer Virus”, noting that “a virus can spread throughout a computer system or network using the authorizations of every user using it to infect their programs. Every program that gets infected may also act as a virus and thus the infection grows.” Computer viruses, as we know them now, originated in 1986 with the creation of Brain – the first virus for personal computers. Two brothers wrote it (Basid and Farooq Alvi who ran a small software house in Lahore, Pakistan) and started the race between viruses and anti-virus programs which still goes on today.
Using the above explanation, it can be said that viruses infect program files. However, viruses can also infect certain types of data files, specifically those types of data files that support executable content, for example, files created in Microsoft Office programs that rely on macros.
Compounding the definition difficulty, viruses also exist that demonstrate a similar ability to infect data files that don’t typically support executable content – for example, Adobe PDF files, widely used for document sharing, and .JPG image files. However, in both cases, the respective virus has a dependency on an outside executable and thus neither virus can be considered more than a simple ‘proof of concept’. In other cases, the data files themselves may not be infectable, but can allow for the introduction of viral code. Specifically, vulnerabilities in certain products can allow data files to be manipulated in such a way that it will cause the host program to become unstable, after which malicious code can be introduced to the system. These examples are given simply to note that viruses no longer relegate themselves to simply infecting program files, as was the case when Mr. Cohen first defined the term. Thus, to simplify and modernize, it can be safely stated that a virus infects other files, whether program or data.
Computer viruses are called viruses because they share some of the traits of biological viruses. A computer virus passes from computer to computer like a biological virus passes from person to person.
There are similarities at a deeper level, as well. A biological virus is not a living thing. A virus is a fragment of DNA inside a protective jacket. Unlike a cell, a virus has no way to do anything or to reproduce by itself — it is not alive. Instead, a biological virus must inject its DNA into a cell. The viral DNA then uses the cell’s existing machinery to reproduce itself. In some cases, the cell fills with new viral particles until it bursts, releasing the virus. In other cases, the new virus particles bud off the cell one at a time, and the cell remains alive.
A computer virus shares some of these traits. A computer virus must piggyback on top of some other program or document in order to get executed. Once it is running, it is then able to infect other programs or documents. Obviously, the analogy between computer and biological viruses stretches things a bit, but there are enough similarities that the name sticks.
A computer virus is a program that replicates. To do so, it needs to attach itself to other program files (for example, .exe, .com, .dll) and execute whenever the host program executes. Beyond simple replication, a virus almost always seeks to fulfill another purpose: to cause damage.
Called the damage routine, or payload, the destructive portion of a virus can range from overwriting critical information kept on the hard disk’s partition table to scrambling the numbers in the spreadsheets to just taunting the user with sounds, pictures, or obnoxious effects.
It’s worth bearing in mind, however, that even without a ”damage routine”, if viruses are allowed to run unabated then it will continue to propagate–consuming system memory, disk space, slowing network traffic and generally degrading performance. Besides, virus code is often buggy and can also be the source of mysterious system problems that take weeks to understand. So, whether a virus is harmful or not, its presence on the system can lead to instability and should not be tolerated.
Some viruses, in conjunction with "logic bombs," do not make their presence known for months. Instead of causing damage right away, these viruses do nothing but replicate–until the preordained trigger day or event when they unleash their damage routines on the host system or across a network.

Impact of Viruses on Computer Systems
Virus can be reprogrammed to do many kinds of harm including the following.
1.Copy themselves to other programs or areas of a disk.
2.Replicate as rapidly and frequently as possible, filling up the infected system’s disk and memory rendering the systems useless.
3.Display information on the screen.
4.Modify, corrupt or destroy selected files.
5.Erase the contents of entire disks.
6.Lie dormant for a specified time or until a given condition is met, and then become active.
7.Open a back door to the infected system that allows someone else to access and even control of the system through a network or internet connection.
8.Some viruses can crash the system by causing some programs (typically Windows) to behave oddly.
How viruses spread from one system to another?
The most likely virus entry points are email, Internet and network connections, floppy disk drives, and modems or other serial or parallel port connections. In today’s increasingly interconnected workplace (Internet, intranet, shared drives, removable drives, and email), virus outbreaks now can spread faster and wider than ever before.

The following are some common ways for a virus to enter the users’ computer system:
•Email attachments
•Malicious scripts in web pages or HTML email
•FTP traffic from the Internet (file downloads)
•Shared network files & network traffic in general
•Demonstration software
•Pirated software
•Shrink-wrapped, production programs (rare)
•Computer labs
•Electronic bulletin boards (BBS)
•Diskette swapping (using other people’s diskettes for carrying data and programs back and forth)

High risk files

The most dangerous files types are:
.EXE, .COM, .XLS, .DOC, .MDB
Because they don’t need any special conversion to infect a computer — all they’ve got to do is run and consequently the virus spreads. It has been estimated that 99% of all viruses are written for these file formats.
A list of possible virus carriers includes:
EXE – (Executable file)
SYS – (Executable file)
COM – (Executable file)
DOC – (Microsoft Word)
XLS – (Microsoft Excel)
MDB – (Microsoft Access)
ZIP – (Compressed file, common in the USA)
ARJ – (Compressed file, common in the USA)
DRV – (Device driver)
BIN – (Common boot sector image file)
SCR – (Microsoft screen saver)

Common Symptoms Of Virus Infection

Computer does not boot.
Computer hard drive space is reduced.
Applications will not load.
An application takes longer to load than normal time period.
Hard dive activity increases especially when nothing is being done on the computer.
An anti virus software message appears.
The number of hard drive bad sectors steadily increases.
Unusual graphics or messages appear on the screen
Files are missing (deleted)
A message appears that hard drive cannot be detected or recognized.
Strange sounds come from the computer.
Some viruses take control of the keyboard and occasionally substitute a neighboring key for the one actually pressed. Another virus "swallows" key presses so that nothing appears on the screen.
Also interesting are system time effects. Clocks going backwards are especially frightening for workers who cannot wait to go home. More seriously though, this type of virus can cause chaos for programs which depend on the system time or date.
Some viruses can cost the user dearly by dialing out on his modem. We do not know of one which dials premium telephone numbers but no doubt we shall see one soon. One particularly malicious virus dials 911 (the emergency number in the USA) and takes up the valuable time of the emergency services.

Categories of viruses
Depending on the source of information different types of viruses may be categorized in the following ways:

PDA VIRUSES
The increasing power of PDAs has spawned a new breed of viruses. Maliciously creative programmers have leveraged the PDA’s ability to communicate with other devices and run programs, to cause digital mayhem.
The blissfully safe world where users of these devices could synchronize and download with impunity came to an end in August 2000 with the discovery of the virus Palm Liberty. Since then, many more viruses have been discovered.
Though not yet as harmful as their PC-based cousins, these viruses still pose a threat to unsuspecting users. Their effects vary from the harmless flashing of an unwanted message or an increase in power consumption, to the deletion of all installed programs. But the threat is growing, and the destructiveness of these viruses is expected to parallel the development of the devices they attack.

MULTIPARTITE VIRUSES
A virus that combines two or more different infection methods is called a multipartite virus. This type of virus can infect both files and boot sector of a disk. Multi-partite viruses share some of the characteristics of boot sector viruses and file viruses: They can infect .com files, .exe files, and the boot sector of the computer’s hard drive. On a computer booted up with an infected diskette, the typical multi-partite virus will first make itself resident in memory then infect the boot sector of the hard drive. From there, the virus may infect a PC’s entire environment. Not many forms of this virus class actually exist. However, they do account for a disproportionately large percentage of all infections. Tequila and Anticad are the examples of multipartite viruses.

BOMBS
The two most prevalent types of bombs are time bombs and logic bombs. A time bomb hides on the victim’s disk and waits until a specific date before running. A logic bomb may be activated by a date, a change to a file, or a particular action taken by a user or a program. Bombs are treated as viruses because they can cause damage or disruption to a system.

BOOT SECTOR VIRUSES
Until the mid-1990s, boot sector viruses were the most prevalent virus type, spreading primarily in the 16-bit DOS world via floppy disk. Boot sector viruses infect the boot sector on a floppy disk and spread to a user’s hard disk, and can also infect the master boot record (MBR) on a user’s hard drive. Once the MBR or boot sector on the hard drive is infected, the virus attempts to infect the boot sector of every floppy disk that is inserted into the computer and accessed. Examples of boot sector viruses are Michelangelo, Satria and Keydrop.
Boot sector viruses work like this: Let us assume that the user received a diskette with an infected boot sector. The user copied data from it but forgot to remove it from drive A:. When he started the computer next time the boot process will execute the infected boot sector program from the diskette. The virus will load first and infect the hard disk. Note that this can be prevented by changing the boot sequence in CMOS (Let C: drive boot before A:). By hiding on the first sector of a disk, the virus is loaded into memory before the system files are loaded. This allows it to gain complete control of DOS interrupts and in the process replaces the original contents of the MBR or DOS boot sector with their own contents and move the original boot sector data to another area on the disk. Because the virus has infected a system area of the hard disk it will be loaded into memory each time the computer is started. It will first take control of the lowest level disk system services before executing the original boot sector code which it has stored in another part of the hard disk. The computer seems to behave exactly as it should. Nobody will notice the extra few fractions of a second added to the boot sequence.
During normal operation the virus will happily stay in memory. Thanks to the fact that it has control of the disk services it can easily monitor requests for disk access – including diskettes. As soon as it gets a request for access to a diskette it will determine that there is a diskette in the floppy drive. It will then examine its boot sector to see if it has already been infected. If it finds the diskette clean it will replace the boot sector with its own code. From this moment the diskette will be a "carrier" and become a medium for infections on other PC’s.

The virus will also monitor special disk requests for access to the boot sector. The boot sector contains its own code, and a request to read it could be from an anti-virus program checking for virus presence. The virus will not allow the boot sector to be read and will redirect all requests to the place on the hard disk where it has backed up the original contents. In this way nothing unusual is detected. Such methods are called stealth techniques and their main goal is to mask the presence of the virus. Not all boot viruses use stealth but those which do are common.
Boot viruses also infect the non-file (system) areas of hard and floppy disks. These areas offer an efficient way for a virus to spread from one computer to another. Boot viruses have achieved a higher degree of success than program viruses in infecting their targets and spreading.
Boot virus can infect DOS, Windows 3.x, Windows 95/98, Windows NT, and even Novell Netware systems. This is because they exploit inherent features of the computer (rather than the operating system) to spread and activate.
Cleaning up a boot sector virus can be performed by booting the machine from an uninfected floppy system disk rather than from the hard drive, or by finding the original boot sector and replacing it in the correct location on the disk.

CLUSTER VIRUSES
This type of virus makes changes to a disks file system. If any program is run from the infected disk, the program causes the virus to run as well. This technique creates the illusion that the virus has infected every program on the disk.

E-MAIL VIRUSES
These types of viruses can be transmitted via e-mail messages sent across private networks or the internet. Some e-mail viruses are transmitted as an infected attachment- a document file or program that is attached to the message. This type of virus is run when the victim opens the file that is attached to the message. Other types of email viruses reside within the body of the message itself. To store a virus, the message must be encoded in html format. Once launched many e-mail viruses attempt to spread by sending messages to everyone in the victim’s address book; each of those contains a copy of the virus.
The latest thing in the world of computer viruses is the e-mail virus called Melissa virus which surfaced in March 1999. Melissa spread in Microsoft Word documents sent via e-mail, and it worked like this:
Someone created the virus as a Word document uploaded to an Internet newsgroup. Anyone who downloaded the document and opened it would trigger the virus. The virus would then send the document (and therefore itself) in an e-mail message to the first 50 people in the person’s address book. The e-mail message contained a friendly note that included the person’s name, so the recipient would open the document thinking it was harmless. The virus would then create 50 new messages from the recipient’s machine. As a result, the Melissa virus was the fastest-spreading virus ever seen and it forced a number of large companies to shut down their e-mail systems at that time.
The ILOVEYOU virus, which appeared on May 4, 2000, was even simpler. It contained a piece of code as an attachment. People who double clicked on the attachment allowed the code to execute. The code sent copies of itself to everyone in the victim’s address book and then started corrupting files on the victim’s machine. This is as simple as a virus can get. It is really more of a Trojan horse distributed by e-mail than it is a virus.
The Melissa virus took advantage of the programming language built into Microsoft Word called VBA, or Visual Basic for Applications. It is a complete programming language and it can be programmed to do things like modify files and send e-mail messages. It also has a useful but dangerous auto-execute feature. A programmer can insert a program into a document that runs instantly whenever the document is opened. This is how the Melissa virus was programmed. Anyone who opened a document infected with Melissa would immediately activate the virus. It would send the 50 e-mails, and then infect a central file called NORMAL.DOT so that any file saved later would also contain the virus! It created a huge mess.
FILE INFECTING VIRUSES
File infectors operate in memory and usually infect executable files with the following extensions: *.COM, *.EXE, *.DRV, *.DLL, *.BIN, *.OVL, *.SYS. They activate every time the infected file is executed by copying themselves into other executable files and can remain in memory long after the virus has activated.
Thousands of different file infecting viruses exist, but similar to boot sector viruses, the vast majority operates in a DOS 16-bit environment. Some, however, have successfully infected the Microsoft Windows, IBM OS/2, and Apple Computer Macintosh environments.
File viruses can be separated further into sub-categories by the way they manipulate their targets:

TSR FILE VIRUSES
A less common type of virus is the terminate-and-stay-resident file virus. As the name suggests these infect files usually these are .com and .exe files. there are however some device driver viruses, some viruses that infect overlay files, and although over 99% of executable programs have the extension .com and .exe, some do not .For a TSR virus to spread some one has to run an infected program. The virus goes memory resident typically looking at each program run thereafter and infects it. Examples of TSR file viruses are Dark Avenger and Green Caterpillar.

OVERWRITING VIRUSES
These viruses infect by overwriting part of their target with their own code but, by doing so, they damage the file. The file will never serve another purpose other than spreading the virus further. Because of this they are usually detected quickly and do not spread easily.

PARASITIC VIRUSES
These viruses attach themselves to executables without substantially changing the contents of the host program. They attach by adding their code to the beginning, end, or even middle of the file and divert program flow so that the virus is executed first. When the virus has finished its job, control is passed on to the host. Execution of the host is a little delayed but this is usually not noticeable.

MACRO VIRUSES
Many older applications had simple macro systems that allowed the user to record a sequence of operations within the application and associate them with a specific keystroke. Later, the user could perform the same sequence of operations by merely hitting the specified key.
Newer applications provide much more complex macro systems. User can write entire macro-programs that run within the word processor or spreadsheet environment and are attached directly onto word processing and spreadsheet files. Unfortunately, this ability also makes it possible to create macro viruses.
Macro viruses currently account for about 80 percent of all viruses, according to the International Computer Security Association (ICSA), and are the fastest growing viruses in computer history. Unlike other virus types, macro viruses aren’t specific to an operating system and spread with ease via email attachments, floppy disks, Web downloads, file transfers, and cooperative applications.
Macro viruses are, however, application-specific. A macro virus is designed to infect a specific type of document file, such as Microsoft word or excel files. They infect macro utilities that accompany such applications as Microsoft Word and Excel, which means a Word macro virus cannot infect an Excel document and vice versa. A macro virus is embedded in a document file and can travel between data files in the application and can eventually infect hundreds of files if undeterred and in the process do various levels of damage to data from corrupting documents to deleting data.
Macro viruses are written in "every man’s programming language" — Visual Basic — and are relatively easy to create. They can infect at different points during a file’s use, for example, when it is opened, saved, closed, or deleted
A typical chronology for macro virus infection begins when an infected document or spreadsheet is loaded. The application also loads any accompanying macros that are attached to the file. If one or more of the macros meet certain criteria, the application will also immediately execute these macros. Macro viruses rely upon this auto-execution capability to gain control of the application’s macro system.
Once the macro virus has been loaded and executed, it waits for the user to edit a new document, and then kicks into action again. It attaches its virus macro programs onto the new document, and then allows the application to save the document normally. In this fashion, the virus spreads to another file and does so in a completely discrete fashion. Users have no idea of the infection. If this new file is later opened on another computer, the virus will once again load, be launched by the application, and find other unsuspecting files to infect.

Finally, as far as a macro virus is concerned, the application serves as the operating system. A single macro virus can spread to any of the platforms on which the application is installed and running. For example, a single macro virus that uses Microsoft Word could conceivably spread to Windows 3.x, Windows 95/98, Window NT, and the Macintosh.

Macro viruses for Word

In the summer of 1995, Microsoft Word 6 was the first product affected with macro virus. The first one (WM/Concept.A) was really only a proof of concept – one of the installed macros (called Payload) contained only this remark:
“That’s enough to prove my point”
Most macro viruses for Word use a feature called ‘automacros’. The basic principle is that some macros with special names are automatically executed when Word starts, opens a file, or closes a file. The macro virus then inserts macros into NORMAL.DOT – a standard template which is loaded every time Word starts.
In Word there are some ways to disable automacros but this isn’t the ultimate solution. Some macro viruses use other methods to take control over the Word environment.
Another method of self-protection may be to set NORMAL.DOT to read only. But this can also be bypassed and, in addition, it prevents the user from customizing the template.

Macro viruses for Excel

Excel has the same opportunities for virus authors as Word. It has automacros and a directory called XLSTART from which templates are automatically loaded.
But Excel does not have just normal VBA macros like Word. In Excel there are so called ‘formulas’ – macros stored in spreadsheet cells. The first macro virus using this technology was XF/Paix.

Macro viruses for other MS Office products:

Writing a macro virus for other Office products is not difficult. There have been already some viruses for Access, and it is expected that there will be macro viruses for Power Point in the near future.

But those macro viruses are not as dangerous as the macro viruses for Word or Excel. Not because of some limitation of these other Office products, but because data files from these products are not so frequently shared.

There is one danger which can be seen in today’s Power Point even without native macro viruses written for this product. Programmers can include in their presentation any number of objects from Excel or Word. And these objects can be infected with macro viruses – if they edit the presentation and open the infected object with its parent application, then the virus can spread further.

But the current situation may change dramatically over the next few years. Microsoft has licensed VBA technology to many firms, so one can expect to see more macro viruses for other products, too.

POLYMORPHIC VIRUSES
This type of virus can change itself each time it is copied, making it difficult to isolate. Most simple viruses attach identical copies of themselves to the files they infect. An anti-virus program can detect the virus’s code (or signature) because it is always the same and quickly ferret out the virus. To avoid such easy detection, polymorphic viruses operate somewhat differently. Unlike the simple virus, when a polymorphic virus infects a program, it scrambles its virus code in the program body. This scrambling means that no two infections look the same, making detection more difficult. These viruses create a new decryption routine each time they infect, so every infected file will have a different sequence of virus code.

STEALTH VIRUSES
Stealth viruses actively seek to conceal themselves from attempts to detect or remove them. They also can conceal changes they make to other files, hiding the damage from the user and the operating system.
Stealth viruses, or Interrupt Interceptors, as they are sometimes called, take control of key DOS-level instructions by intercepting the interrupt table, which is located at the beginning of memory. This gives the virus the ability to do two important things: 1) gain control of the system by re-directing the interrupt calls, and 2) hide itself to prevent detection. They use techniques such as intercepting disk reads to provide an uninfected copy of the original item in place of the infected copy (read-stealthing viruses), altering disk directory or folder data for infected program files (size-stealthing), or both. For example, the Whale virus is a size-stealthing virus. It infects .EXE program files and alters the folder entries of infected files when other programs attempt to read them. The Whale virus adds 9216 bytes to an infected file. Because changes in file size are an indication that a virus might be present, the virus then subtracts the same number of bytes (9216) from the file size given in the directory/folder entry to trick the user into believing that the file’s size has not changed.
An antivirus program which is not equipped with anti-stealth technology will be deceived.

COMPANION VIRUSES

A companion virus is the exception to the rule that a virus must attach itself to a file. The companion virus instead creates a new file and relies on a behavior of DOS to execute it instead of the program file that is normally executed. These viruses target EXE programs. They create another file of the same name but with a COM extension containing the virus code. These viruses take advantage of a property of MS-DOS which allows files to share the same first name in the same directory (e.g. ABC.EXE and ABC.COM) but executes COM files in preference to EXE files.
For example, the companion virus might create a file named CHKDSK.COM and place it in the same directory as CHKDSK.EXE. Whenever DOS must choose between executing two files of the same name where one has an .EXE extension and the other a .COM extension, it executes the .COM file. This is not an effective way of spreading but has one big advantage – it does not amend files in any way and so can escape integrity tests or resident protection. Another method which can be used by companion viruses is based on defined path. A virus simply puts an infected file into the path listed before the directory within the original program.

PROGRAM VIRUSES
Like normal programs, program viruses must be written for a specific operating system. The vast majority of viruses are written for DOS but some have been written for Windows 3.x, Windows 95/98, and even UNIX. All versions of Windows are compatible with DOS and can host DOS viruses with varying degrees of success. Program viruses infect program files, which commonly have extensions such as .COM, .EXE, .SYS, .DLL, .OVL, or .SCR. Program files are attractive targets for virus writers because they are widely used and have relatively simple formats to which viruses can attach.

Malicious Programs and Scripts

Viruses that infect agent programs (such as those that download software from the Internet; for example, JAVA and ActiveX).

WORM

A worm is a computer program that has the ability to copy itself from machine to machine. Worms normally move around and infect other machines through computer networks. An entire LAN or corporate e-mail system can become totally clogged with copies of a worm, rendering it useless. Worms are commonly spread over the internet via e-mail message attachments and through internet relay chat channels.
For example, the Code Red worm replicated itself over 250,000 times in approximately nine hours on July 19, 2001.
A worm usually exploits some sort of security hole in a piece of software or the operating system. For example, the Slammer worm (which caused mayhem in January 2003) exploited a hole in Microsoft’s SQL server.
Worms use up computer time and network bandwidth when they are replicating, and they often have some sort of evil intent. A worm called Code Red made huge headlines in 2001. Experts predicted that this worm could clog the Internet so effectively that things would completely grind to a halt.
The Code Red worm slowed down Internet traffic when it began to replicate itself, but not nearly as badly as predicted. Each copy of the worm scanned the Internet for Windows NT or Windows 2000 servers that do not have the Microsoft security patch installed. Each time it found an unsecured server, the worm copied itself to that server. The new copy then scanned for other servers to infect. Depending on the number of unsecured servers, a worm could conceivably create hundreds of thousands of copies.
The Code Red worm was designed to do three things:
•Replicate itself for the first 20 days of each month
•Replace Web pages on infected servers with a page that declares "Hacked by Chinese"
•Launch a concerted attack on the White House Web server in an attempt to overwhelm it
The most common version of Code Red is a variation, typically referred to as a mutated strain, of the original Ida Code Red that replicated itself on July 19, 2001.

TROJAN HORSES

Trojans, another form of malware, are generally agreed upon as doing something other than the user expected, with that “something” defined as malicious. Most often, Trojans are associated with remote access programs that perform illicit operations such as password-stealing or which allow compromised machines to be used for targeted denial of service attacks. One of the more basic forms of a denial of service (DoS) attack involves flooding a target system with so much data, traffic, or commands that it can no longer perform its core functions. When multiple machines are gathered together to launch such an attack, it is known as a distributed denial of service attack, or DDoS.
Because Trojan horses do not make duplicates of themselves on the victims disk (or copy themselves to other disks), they are not technically viruses. But because they can do harm, many experts consider them to be a type of virus. Trojan horses are often used as by hackers to create a back door to an infected system. Trojans, such as BackOrrifice are very dangerous. If anyone runs this program and his computer is connected to the internet, then the hacker can take control of that computer – transfer files to or from the computer, capture screen contents, run any program or kill any running process, etc.

Once a Trojan is installed onto the system this program has the same privileges as the user of the computer and can exploit the system to do something the user did not intend such as:
Delete files
Transmit to the intruder any files that the user can read
Change any files that the user can modify
Install other programs with the user’s privileges
Execute privilege-elevation attacks—the Trojan can attempt to exploit a weakness to raise the level of access beyond the user running the Trojan. If successful, the Trojan can operate with increased privileges.
Install viruses
Install other Trojans

The Following Tips Will Help The User To Minimize Virus Risk:

If the users are truly worried about traditional (as opposed to e-mail) viruses, they should be running a more secure operating system like UNIX. One should never hear about viruses on these operating systems because the security features keep viruses (and unwanted human visitors) away from the hard disk.
If the users are using an unsecured operating system, then buying virus protection software is a nice safeguard. Some popular anti virus programs include:
•McAfee Virus Scan
•Norton Anti Virus
•Virex
•PC—cillin
•Avast!
•AVG Anti Virus System
Automatic protection of anti-virus software should be turned on at all times.
The users should perform a manual scan (or schedule a scan to occur automatically) of their hard disks weekly. These scans supplement automatic protection and confirm that the computer is virus-free.
Scan all floppy disks before first use.
Disable floppy disk booting — most computers now allow the user to do this, and that will eliminate the risk of a boot sector virus coming in from a floppy disk accidentally left in the drive.
The users should Enable Automatic Update option of their anti-virus software in order to update their virus definition files.
Creation and maintenance of a rescue disk should be done by the user in order to facilitate recovery from certain boot viruses.
Periodic backups of the hard disk should be done.
Users’ should buy legal copies of all software they use and make write-protected backups.
 Email messages and email attachments from unknown people should not be opened. Attachments that come in as Word files (.DOC), spreadsheets (.XLS), images (.GIF and .JPG), etc., are data files and they can do no damage (noting the macro virus problem in Word and Excel documents mentioned above). A file with an extension like EXE, COM or VBS is an executable, and an executable can do any sort of damage it wants. Further it should be verified that the "author" of the email has sent the attachments. Newer viruses can send email messages that appear to be from a person user know.
The potential users should make sure that Macro Virus Protection is enabled in all Microsoft applications, and they should never run macros in a document unless they know specifically the functionality of the macros.
Appropriate Passwords should be assigned to the shared network drives.

Things that are not viruses!

Joke programs
Joke programs are not viruses and do not inflict any damage. Their purpose is to frighten their victims into thinking that a virus has infected and damaged their system. For example, a joke program may display a message warning the user not to touch any keys or else the computer’s hard disk will be formatted.

Droppers
A dropper is a program that is not a virus, nor is it infected with a virus but when run it installs a virus into memory on to the disk, or onto a file. Droppers have been written sometimes as a convenient carrier for a virus and sometimes as an act of sabotage.

Hoaxes
There must be very few people on email who haven’t received a chain letter with the subject line warning of a virus doing the rounds. These are often hoaxes and meant to scare people and have fun at their expense. The warnings encourage the recipient of the e-mail to pass the warning to the netizens and thus create an unnecessary furor, besides clogging mailboxes, as it usurps an air of credibility.

Methodology of virus detection applied by antivirus softwares:

Three main methods exist for detecting viruses: integrity checking (also known as checksumming), behavior monitoring and pattern matching (scanning).

Integrity checking
Antivirus programs that use integrity checking start by building an initial record of the status (size, time, date, etc.) of every application file on the hard drive. Using this data, checksumming programs then monitor the files to see if changes have been made. If the status changes, the integrity checker warns the user of a possible virus.
However, this method has several disadvantages, the biggest being that false alarms are altogether too common. The records used by checksumming programs are often rendered obsolete by legitimate programs, which, in their normal course of operations, make changes to files that appear to the Integrity checker to be viral activity. Another weakness of integrity checking is that it can only alert the user after a virus has infected the system.

Behavior monitoring
Behavior Monitoring programs are usually terminate and stay resident (TSR) and constantly monitor requests that are passed to the interrupt table. These programs are on the lookout for activities that a virus might engage in–requests to write to a boot sector, opening an executable program for writing, or placing itself resident in memory. The behavior these programs monitor is derived from a user-configurable set of rules.

Pattern matching
Using a process called "pattern matching," the anti-virus software draws upon an extensive database of virus patterns to identify known virus signatures, or telltale snippets of virus code. Key areas of each scanned file are compared against the list of thousands of virus signatures that the anti-virus software has on record.
Whenever a match occurs, the anti-virus software takes the action the user has configured: Clean, Delete, Quarantine, Pass (Deny Access for Real-time Scan), or Rename.

Self Defense Mechanisms Evolved By Viruses

Virus authors of course wish that their child successfully lives. For this reason there are many viruses outfitted with some self-defense mechanisms against anti virus systems.

Passive Defense :
Viruses use a variety of methods to hide themselves from antivirus programs. Passive defense uses programming methods which make analysis of the virus more difficult, e.g. polymorphic viruses which were developed to counter scanners looking for constant strings of virus code.
Today antivirus systems are capable of analyzing polymorphic code and searching for virus identifiers in the decrypted body. The virus authors reacted by making the encryption too complex for antivirus software to unravel, thus mistaking it for a clean program.

Active Self-defense :
Viruses actively defend themselves by protecting their own code or by attempting to damage antivirus software. A simple method is to locate antivirus software databases and amend or delete them.
More sophisticated resident viruses use stealth techniques. When they detect a request to use an infected file, they can temporarily "clean" it or report its original (uninfected) parameters. They can monitor which programs are being executed and react if it is antivirus software. The list of such reactions is endless. Usually, the execution of the antivirus program is refused, but it could be erased (often accompanied by a bogus error message) or the virus suspends its activities while it runs. There are occasionally extremely ‘clever’ viruses which modify the code of a specific AV program to partially disable it.
There are very rare viruses which consider an attempt to run an anti-virus program as arrogant and immediately reply with some revenge action – for example hard disk formatting.

Trap
A trap is the most malicious form of self-defense and works as follows. Although the user’s computer is infected but everything appears to work correctly. Once the user discovers the virus and removes it things get complicated – programs no longer run properly or the hard disk may become inaccessible even when booting from a clean system diskette.
The best known trap virus is One_Half. It continuously encrypts the data on a hard disk (two tracks on every boot). If it is removed from the partition sector before data files are decoded then some files will become inaccessible. At this stage the situation is serious but recovery of the data is still possible. However, if the user runs a disk utility (Scandisk etc.) to repair the damage then the data will almost certainly be lost forever.
These utilities are designed to repair relatively minor damage to file system and do not recognize the encrypted data.

REFERENCE:

1. Mary Landesman “What is a virus?”
http://antivirus.about.com/cs/tutorials/a/whatisavirus.htm
2. NetGuide “What are computer viruses? “–
http://www.netguide.co.nz/knowhow/tutorials/print.php?iid=38
3. Marshall Brain “How Computer Viruses Work”
http://www.Howstuffworks How Computer Viruses Work.htm
4. AVG Anti Virus Free Edition Help
Developed by Grisoft Inc
5. Norton Anti-virus Help
Developed by Symantec Corporation
6. Trend Micro PC-cillin Help
Developed by Trend Micro Inc
7. Peter Norton “Computer Viruses”
Introduction to Computers, Tata McGraw Hill Co:
8. Dr.Solomon ”About Viruses” &”Virus Prevention”
Dr.Solomon’s Virus Encyclopedia, Dr.Solomon’s Software Ltd.
9. C.A.Schmidt ”Virus”
The Complete Computer Upgrade And Repair Text Book,Dreamtech
10. S.Jaiswal “Virus Detection And Elimination”
Information Technology Today, Galgotia Publication Pvt. Ltd.

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M.Com,M.C.A, Master in Multimedia Development (Equiv: M.E)
Lecturer-Pailan School of International Studies
Part time Lecturer -Prafulla Chandra College