This is in contrast to an operative with official cover, where they assume a position in their government, such as the diplomatic service, which provides them with diplomatic immunity if their espionage activities are discovered. Operatives under non-official cover do not have this "safety net", and if captured and charged as spies are subject to severe criminal punishments, up to and including execution. Operatives under non-official cover are also usually trained to deny any connection with their government, thus preserving plausible deniability, but also denying them any hope of diplomatic legal assistance – or official acknowledgment of their service. Such an operative or agent may be referred to as a NOC (pronounced // NOK) or as an illegal (see Clandestine HUMINT operational techniques). Sometimes, entire front companies or strawman entities are established in order to provide false identities for agents.
An agent sent to spy on a foreign country might, for instance, work as a businessperson, a worker for a non-profit organization (such as a humanitarian group), or an academic. For example, the CIA's Ishmael Jones spent nearly two decades as a NOC.
Many of the agents memorialized without names or dates of service on the CIA Memorial Wall are assumed to have been killed or executed in a foreign country while serving as NOC agents. In nations with established and well-developed spy agencies, the majority of captured non-native NOC agents have, however, historically been repatriated through prisoner exchanges for other captured NOCs as a form of gentlemen's agreement.
Some countries have regulations regarding the use of non-official cover: the CIA, for example, has at times been prohibited from disguising agents as members of certain aid organizations, or as members of the clergy.
The degree of sophistication put into non-official cover stories varies considerably. Sometimes, an agent will simply be appointed to a position in a well-established company which can provide the appropriate opportunities. Other times, entire front companies can be established in order to provide false identities for agents.
Former MI6 officer "Nicholas Anderson" wrote an account of his service in a fictionalized autobiography (as per British law) entitled NOC: Non-Official Cover: British Secret Operations, and two sequels: NOC Twice: More UK Non-Official Cover Operations and NOC Three Times: Knock-On Effect (Last of the Trilogy).
Michael Ross, a former Mossad officer, operated as a Mossad NOC or "combatant" as described in his memoir, The Volunteer: The Incredible True Story of an Israeli Spy on the Trail of International Terrorists (Skyhorse Publishing, September 2007, ISBN 978-1-60239-132-1).
Fictional notable examples include Chuck Barris who made a satirical claim to have been a NOC with 33 kills in his book and movie Confessions of a Dangerous Mind. Other examples are featured in the books Debt of Honor and The Eleventh Commandment; the films Mission: Impossible, Spy Game, The Bourne Identity, Safe House, and The Recruit; and the television shows The Americans, Burn Notice, Spooks, The Night Manager, Covert Affairs, and Patriot.
- Shannon, Elaine (February 20, 1995). "Spies for the New Disorder". Time. Retrieved 2008-02-19.
- John Weisman (September 7, 2010). "Tripping Over CIA's Bureaucratic Hurdles". Washington Times. Retrieved 2010-03-19.
- "Dr Udo Ulfkotte, journalist and author, on RT". September 29, 2014.
- "Our Kind of Traitor: an interview with former MI6 intelligence officer Nicholas Anderson". historyextra.com. Immediate Media Company. May 11, 2016. Retrieved February 21, 2018.