Blacklist
A blacklist is list of items, such as usernames or IP addresses, that are denied access to a certain system or protocol. When a blacklist is used for access control, all entities are allowed access, except those listed in the blacklist. The opposite of a blacklist is a whitelist, which denies access to all items, except those included in the list.
Blacklists have several applications in computing:
Web servers often include a blacklist that denies access from specific IP addresses or ranges of IPs, for security purposes.
Firewalls may use a blacklist to deny access to individual users, systems located in certain regions, or computers with IPs within a certain subnet mask.
Spam filters often include blacklists that reject certain e-mail addresses and specific message content.
Programmers may implement blacklists within programs to prevent certain objects from being modified.
Since blacklists deny access to specific entities, they are best used when a limited number of items need to be denied access. When most entities need to be denied access, a whitelist approach is more efficient.
Updated September 28, 2010 by Per C.
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