Mal ware includes computer viruses, worms, Trojan horses, and also spy ware.

Viruses self-replicate within computers and across networks and alter files or data. Worms are a virus variant that can infect a computer without any user interaction. Trojans are malicious coding hidden in within innocuous programming or data in such a way that it can get control and do its chosen form of damage, such as destroying the contents of a hard disk. Spy ware is programming that is put into your computer to secretly gather information and relay it to advertisers or other interested parties.

Mal ware is distributed by e-mail, (through a attachment or code inside the email message body); in an infected application; or through infected code on a Web site. Originally a floppy diskette was required as the vehicle to introduce mal ware to a computer, but now most of the mal ware is distributed electronically. Security experts claim that because security isn't built into Web applications, an attacker can often hack into a site and introduce some mal ware, simply by viewing a Web page's source and viewing its code.

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