A destructive program disguised as a game, utility, or application. When run, a Trojan horse does something harmful to the computer system while appearing to do something useful. See also virus, worm.
A large hollow wooden figure of a horse (filled with Greek soldiers) left by the Greeks outside Troy during the Trojan War; Also called: Wooden Horse.
In computing, a virus program that appears to function normally but, while undetected by the normal user, causes damage to other files or circumvents security procedures.
The earliest appeared in the UK in about 1988.

Seemingly innocuous but treacherous gift from an enemy. In Greek mythology, during the siege of Troy, an enormous wooden horse left by the Greek army outside the gates of the city. When the Greeks had retreated, the Trojans, believing it to be a religious offering, brought the horse in. Greek soldiers then emerged from within the hollow horse and opened the city gates to enable Troy to be captured.