Common terms used in computer security:
Virus: A program that replicates itself across a network or the Internet as a whole. The virus payload may be destructive, like deleting files, or it could simply try to overwhelm a network by copying itself.
Worm: A virus that replicates itself without human intervention. If the victim has to open an e-mail attachment to get infected, it's a virus. But if it scans for new victims and attacks by itself, it's a worm.
Trojan horse: A program that doesn't necessarily replicate itself, but like the legendary wooden horse is much more than it appears. A Trojan horse program might look like a game, but instead it steals your personal information and sends it to a criminal.
Password sniffer: A file that seeks out passwords on your computer, then sends them to a hacker. A keylogger can also grab anything typed on the keyboard.
Blended threat: A program that combines the characteristics of viruses, worms and Trojan horses. A blended threat, like the recent Nimda outbreak, is a recent phenomenon.
Exploit: A program that takes advantage of a security hole in a computer program, like Microsoft Windows or AOL Instant Messenger.
Spyware: A general term for a program that surreptitiously monitors your actions. While they are sometimes sinister, like a remote control program used by a hacker, software companies have been known to use spyware to gather data about customers. The practice is generally frowned upon.
Virus signature: The "fingerprints" of a virus, which antivirus programs use to identify and isolate viruses. Users should regularly update their antivirus programs online to download the latest virus signatures, so they're protected against new viruses.
Firewall: Software that monitors incoming and outgoing Internet traffic to your computer and checks for suspicious patterns. A firewall may alert you to spyware or a Trojan horse installed on your computer.