infiltrator

nouns

someone who takes up a position surreptitiously for the purpose of espionage

is derived from

is a type of (narrower)

(military) a secret agent hired by a state to obtain information about its enemies or by a business to obtain industrial secrets from competitors

an intruder (as troops) with hostile intent

infiltrator

is derived from

is a type of (narrower)

someone who intrudes on the privacy or property of another without permission