Trojans

Trojans were named after the Trojan Horse of Greek mythology.  According to the story, a large wooden horse was delivered to the city of Troy. The city's people considered it a gift, so  they brought it inside the city walls.  When the horse was brought inside, the Greek army jumped out of the horse in which they had been hiding.  The Greek army took control of the city of Troy.

Trojans took this name because they are programs that appear to be useful but, in fact, are hiding something that will damage the computer.  A trojan is any program that looks useful but causes damage and does not replicate.  Since trojans can't replicate, they are less abundant than viruses.  A trojan must be transferred to each computer separately and is often carried by a virus, worm, or even a hoax to do this.  Many are sent as e-mail attachments

EXAMPLES

In 1989, there were 20,000 copies of an AIDS information disk were mailed to the public.  The disk turned out to be a trojan.  Anyone who inserted the disk was infected with the trojan.  Then, after the system was rebooted 90 times, the trojan renamed and hide all of the files on the hard disk.

PictureNote is another example of a trojan.  It is sent through the e-mail as an e-mail attachment named PICTURE.EXE.  When this file is opened, the trojan steals America OnLine user information and sends it to an unknown source.