Hoax – An e-mail that usually states that it is harming the computer, but does not actually do what it says. Some hoaxes ask the reader of the e-mail to perform a damaging process, such as deleting an important file. Most hoaxes are spread by people who do not know that the e-mail is a hoax and who are hoping to alert others to a potential virus.

Trojan or Trojan Horse – A software program usually created to make a computer less secure. The software usually looks similar to a useful file that a person would want to open. The payload of a Trojan is usually delivered when the file opens and usually has devastating results. Trojans are often used to create back-doors (a program that allows outside access into a secure network). Trojans are most often delivered as an e-mail attachment or through security vulnerabilities while browsing the Internet.

Virus – A software program that copies itself into another program, a hidden space on a drive, or items that support scripts. Most viruses copy only themselves, while a minority unleash a payload – actions caused by the virus. Payloads can damage files, deliver Trojan files, corrupt hard drives, display messages, or open other files. Typically, payloads deliver when a certain condition occurs, such as when the date on the computer reaches a particular day.

A virus variant is a virus that has been altered to take advantage of the original virus code. By doing this, the virus variant is easier to create, creating more virus versions.

Worm – Another form of virus that finds vulnerable computers and copies itself to those systems. The most frequent methods of propagation are from e-mail distribution lists, e-mail signature scripts, and shared folders on the network. Worms might or might not have a damaging payload. The typical payload for a worm makes a computer more susceptible to other viruses and Trojans.