| | | | A piece of code or a program that is able to replicate itself without the conscious intervention of the user of the "host" machine. The term is commonly used to refer to any kind of malware, however strictly speaking it means code that attaches itself to another program to replicate itself. The first viruses to be seen by home users arose in the 1980s. A man-made phenomenon, viruses are most commonly activated (statistically) when an email attachment containing one is opened and they are also spread via such methods as bootleg software or software traded illegally on file sharing networks. It may do a number of other things as well as replicating itself, including executing programs, "sending" itself to infect other recipients using the host's email client or network connection (this type of virus is usually referred to as a "worm"), deleting files or installing files. More destructive viruses can even require that the hard drive be reformatted. Even apparently benign viruses still cause a problem for the host machine however, by using up available memory. Viruses may be divided into "resident" and "non-resident" types, depending on what happens when they are executed. Resident viruses are loaded into the computer's memory when executed, upon which control is handed to the host program. The virus then spreads by attaching itself to other applications / programs when they are executed and it remains active in memory. In contrast, non-resident types immediately search for new hosts upon being executed, attach themselves to the new host and only then transfer control to the infected host program. Viruses may also be written for legitimate reasons - for testing purposes when developing antivirus software for example, or to check existing security measures. This situation differs from viruses encountered in the "wild" because the intention when writing them is not malicious. | | | |
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