Denylist (sometimes referred as blocklist, formerly known as blacklist) is a list of sites, programs, or other elements that are not allowed to be started or visited.

Denylists are used to enhance the security of computer systems. An example of a denylist could be:

• A list of email addresses for sending adware. Messages from these addresses are filtered, marked as spam, and/or blocked.

• A list of untrusted Internet resources for which the browser issues a warning when an attempt is made to open them.

• A list of apps banned from being downloaded to a device.

Cybercriminals sometimes use their own denylists to control attacks: some malware code contains IP addresses that are off limits.