Trojan Horse

A type of computer virus disguised as a program. The scenario usually happens like this: a user may download a program from the Net because they think it may be of some use; but once the program is opened (or run), it releases a virus that erases their hard drive or wreaks havoc on their system. A popular Trojan horse virus came in the form of an e-mail attachment of a file called "AOL4FREE.COM," and the "I Love You" virus is another example. The name comes from the Greek legend of a horse that looks benevolent at first, but in actuality harbors trouble.

see also: sniffer , virus.