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

Definitions by TechTerms.com

The definition of Blacklist on this page is an original TechTerms.com definition. If you would like to reference this page or cite this definition, you can use the green citation links above.

The goal of TechTerms.com is to explain computer terminology in a way that is easy to understand. We strive for simplicity and accuracy with every definition we publish. If you have feedback about the Blacklist definition or would like to suggest a new technical term, please contact us.

Want to learn more tech terms? Subscribe to the daily or weekly newsletter and get featured terms and quizzes delivered to your inbox.

Sign up for the free TechTerms Newsletter

How often would you like to receive an email?

You can unsubscribe or change your frequency setting at any time using the links available in each email.

Questions? Please contact us.