double agent

In the field of counterintelligence, a double agent is an employee of a secret intelligence service for one country whose official purpose is to spy on a target organization of another country, but who is now spying on their own country's organization for the target organization.

Double agentry may be practiced by spies of the target organization who infiltrate the primary, controlling organization or may result from the turning (switching sides) of previously loyal agents of the controlling organization by the target. The threat of execution is the most common method of turning a captured agent (working for an intelligence service) into a double agent (working for a foreign intelligence service) or a double agent into a re-doubled agent. The double agent is unlike a defector, who is not considered an agent, as agents are posted to function for an intelligence service and defectors are not, although some consider that defectors have been agents de facto until they have defected.