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A computer virus is an illegal and potentially damaging computer program designed to infect other software by attaching itself to any software it contacts. In many cases, virus programs are designed to damage computer systems maliciously by destroying or corrupting data. If the infected software is transferred to or accessed by another computer system, the virus spreads to the other system. Viruses have become a serious problem in recent years, and currently, thousands of known virus programs exist.
The three main types of viruses are the boot sector virus, the file virus, and the Trojan horse virus. A boot sector virus infects the boot program used to start the system. When the infected boot program executes, the virus is loaded into the computers memory. Once a virus is in a memory, it can spread to any floppy disk inserted into the computer. A file virus inserts virus code into program files. The virus then spreads to any program that accesses the infected file. A Trojan horse virus (named after a Greek myth) hides within or is designed to look like a legitimate program.
Some viruses interrupt processing by freezing a computer system temporarily and then displaying sounds or messages. Other viruses contain time bombs or logic bombs. A time bomb is a program that performs an activity on a particular date. A logic bomb is a program that performs an activity when a certain action occurs, such as an employee being terminated. A worm, which is similar to a virus, copies itself repeatedly until no memory or disc space remains.
To detect computer viruses, antivirus programs have been developed. Besides detecting viruses, antivirus programs also have utilities to remove or repair infected programs and files. Some damaged files cannot be repaired and must be replaced with uninfected backup files.
Some techniques used to protect computer systems include :
Using virus protection software, backing up your computer, before use, scan every floppy disk with a virus scan program to check for viruses and finally, check all programs downloaded from the Internet or bulletin boards for viruses.