Term: Trojan or Trojan horse

Definition: a malicious program that when executed on the recipient's computer will perform some act that is designed to cause damage to the PC. As a rule, Trojan Horse programs do not replicate and spread themselves. Instead, they masquerade as legitimate programs. [However, rules are made to be broken, so this may not always apply.]

Example: An example of a Trojan horse is PictureNote.Trojan. This is a malicious program that searches for AOL user and password information on the infected computer. PictureNote.Trojan can't spread itself, but is usually sent as an email attachment called PICTURE.EXE.

Discussion: Trojans are worse than viruses. As a rule, they are designed to cause damage. Some of these email attachments masquerade as cute or useful little programs; others are written to actually perform some small task. In this way, you think you're running a helpful utility or fun file, when what you're actually doing is bringing the Trojan horse inside the gates of your system. When you execute it, it does something to damage your computer — like erasing your hard drive or blocking your screen with a graphic you can't get rid of. Many of them are designed to capture password or credit card information and email this information (silently so you don't know it's doing it) to a coded email address.