Anti Virus
What is a Computer Virus?
A computer virus is a computer program designed to spread itself by saving copies of itself on any computer disk, hard drive or floppy disk, that it comes in contact with. Viruses usually occur without the knowledge of the user. Some viruses do nothing but replicate themselves, and only cause problems by the space they occupy. Others are programmed to do something destructive such as deleting all the files it can find on a disk, or changing the code files of all the programs on the computer so they will begin to crash.
How do Viruses Spead?
When a program infected by a virus is executed, the virus code will also run, and it will try to infect other programs. This can be done on the same computer or on other computers connected by a network. The new infected programs will try to infect more programs. When a copy of an infected file is shared with other computer users, running the file may also infect their computer, and infected files will continue to spread to more computers. If a computer is infected with a boot sector virus, the virus tries to write copies of itself to the system areas of floppy disks and hard disks. Then the infected floppy disk may infect other computers that boot from them, and the virus copy on the hard disk will try to infect more floppies.
Types of Viruses
Viruses come in many shapes and sizes. These are the most common. File infectors are viruses that attach themselves to regular programs, such as COM or EXE files under DOS. They are applied each time the infected program is run. Cluster infectors modify the file system so that they are run prior to other program. Unlike file infectors, they do not attach themselves to a program. System infectors affect the computer operating systems which set aside a portion of each disk for code to boot the computer. Under DOS, this section is called the boot sector on floppies or the master boot record for a hard disk. System infectors store themselves in this area and are invoked whenever the disk is used to boot the system. Macro viruses are word processing documents that can serve as sources of transmission for viruses that take advantage of the auto-execution macro-capabilities in products such as Microsoft Word. By opening an infected document the virus, written in a product's macro language, can spread. Melissa is the fastest spreading Microsoft macro virus to date. For more information click on
MELISSA
Closely related to computer viruses are trojan horses and worms. A trojan horse is a program that performs some undesired yet intended action while, or in addition to, pretending to do something else. One common class of trojans are fake login programs-collecting accounts and passwords by prompting for this info just like a normal login program does. Another is a disk defragger that erases files rather than reorganizing them. A trojan horse is different from a virus because it does not attempt to reproduce itself. A worm is just a self-propagating virus. An excellent web page for any information regarding viruses, myths and facts is at
Stiller.com
How do Anti-Virus Programs Work
Virus combat programs work by knowing where all these operating system programs are, and how large they are. If a virus has added code to a program it will be a different size and identifiable. The program will then open the identified file, delete the offending code, and save the "cleaned" file. Scanners are also used to detect certain code (signiture strings) of a virus. The scanner takes out these pieces of code. Sometimes this cannot be accomplished without damaging the infected files. That is why it is important to have backup copies of files. There are many other factors to anti-virus software and here is a list of some of the best anti-virus software sites.
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