(Coined by MIT-hacker-turned-NSA-spook Dan Edwards) A malicious, security-breaking program that is disguised as something benign, such as a directory lister, archiver, game, or (in one notorious 1990 case on the Mac) a program to find and destroy viruses! A Trojan horse is similar to a back door.

See also RFC 1135, worm, phage, mockingbird.

[Jargon File]