Iran was apparently forced to reveal its existence after it became aware that western intelligence agencies had known about it for years.

VOA: standard.2009.09.28

And it can also be used by matching against databases already in existence in the intelligence community.

CNN: Facing up to airport security fears

There are intelligence agencies whose very existence is secret, whose charters and budgets are secret, and whose activities include secret paramilitary operations abroad.

CENTERFORSECURITYPOLICY: The Case Against the Halperin Nomination �� White Paper

Many MPs buried their pre-war doubts when assured that existence of the weapons was confirmed by intelligence that could not be disclosed for fear of prejudicing sources.

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