A spy placed in a target area but does not engage in espionage until he or she is activated at a future time.

Walk-In

Someone who voluntarily offers to spy. An unheralded defector or a "dangle, " a walk-in is a potential agent or mole who literally walks into an enemy embassy or intelligence agency without prior contact or recruitment.

During the Decade of the Spy the term was especially applied to Americans who walked into Soviet embassies or other offices and proffered secret information. They included civilians and uniformed men from the Army, Navy, Marines, Air Force, major defense contractors, CIA, NSA, and FBI.