Warrant canary

A warrant canary is a method by which a communications service provider aims to inform its users that the provider has not been served with a secret government subpoena.

Secret subpoenas, such as those covered under 18 U.S.C. §2709(c) of the USA Patriot Act, provide criminal penalties for disclosing the existence of the warrant to any third party, including the service provider's users. A warrant canary may be posted by the provider to inform users of dates that they have not been served a secret subpoena. If the canary is not updated for the time period specified by the host or if the warning is removed, users are to assume that the host has been served with such a subpoena. The intention is to allow the provider to warn users of the existence of a subpoena passively, without disclosing to others that the government has sought or obtained access to information or records under a secret subpoena. Warrant canaries have been found to be legal by the United States Justice Department, so long as they are passive in their notifications.