(1) A list of e-mail addresses of known spammers. See spam, spam filter, Blacklist of Internet Advertisers, greylisting and blackholing. Contrast with white list.

(2) A list of Web sites that are considered off limits or dangerous. A Web site can be placed on a blacklist because it is a fraudulent operation or because it exploits browser vulnerabilities to send spyware and other unwanted software to the user. Contrast with white list.