What are computer viruses?

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What are computer viruses?hijack this

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What are computer viruses?liveupdate

A computer virus is a self-replicating computer program written to alter the way a computer operates, without the permission or knowledge of the user. Though the term is commonly used to refer to a range of malware, a true virus must replicate itself, and must execute itself. The latter criteria is often met by a virus which replaces existing executable files with a virus-infected copy. While viruses can be intentionally destructive鈥攄estroying data, for example鈥攕ome viruses are benign or merely annoying.

Classification of virusses

Viruses can be subdivided into a number of types, the main ones being:

Boot sector viruses

Companion viruses

Email viruses

Logic bombs and time bombs

Macro viruses

Cross-site scripting virus

Two other types of malware are often classified as viruses, even though they may not meet the standard criteria:

Trojan horses

Worms

*Why people create computer viruses

Unlike biological viruses, computer viruses do not simply evolve by themselves. Computer viruses do not come into existence spontaneously, nor are they likely to be created by bugs in regular programs. They are deliberately created by programmers, or by people who use virus creation software. Computer viruses can only do what the programmers have programmed them to do.