The Trojan horse
A type computer viruses was named after this Horse
A Trojan Horse is a type of Computer Virus
According to legend, the Greeks won the Trojan war by hiding in a huge, hollow wooden horse to sneak into the fortified city of Troy. In today's computer world, a Trojan horse is defined as a "malicious, security-breaking program that is disguised as something benign". For example, you download what appears to be a movie or music file, and when you click on it, you unleash a dangerous program that erases your disk, sends your credit card numbers and passwords to a stranger, or lets that stranger hijack your computer to commit illegal denial of service attacks like those that have virtually crippled the DALnet IRC network for months on end.
Unlike a virus or a worm, trojans do not replicate themselves so to get infected you must, one way or another, have downloaded the program onto your computer. This most commonly occurs when you download a program that pretends to be one thing while it is actually another. Hence the origin of the "Trojan" name.