Green’s Dictionary of Slang

(US) pertaining to undercover/intelligence operations.

1967		R. Starnes Requiem in Utopia 145: ‘So it’s to be a spook operation after all?’.
1977		(con. 1969) M. Herr Dispatches 50: It was spookwar then, adventure: not exactly soldiers, not even advisers yet, but Irregulars.
2007		W. Ellis Crooked Little Vein 29: They’d spent the last two years using every paranoia-inducing spook operation you’ve ever heard of.