Walk-in agent
Appearance
A walk-in agent is an individual who voluntarily offers to conduct espionage. Specifically, a "walk-in" is an agent or a mole of a government who literally walks into an embassy or intelligence agency without prior contact or recruitment.
References
Polmar, Norman; Thomas B. Allen (October 1996). Spy Book, The Encyclopedia of Espionage. Random House. ISBN 978-0-679-42514-4.