infiltrated
adj.adj. describing something that has been entered secretly or quietly, often to cause harm or get information. You use this when someone or something has sneaked into a group or place without being noticed.
adj. having entered or gained access to an organisation or place surreptitiously, typically for subversive purposes. Participial adjective; often used predicatively after 'be' or 'become'.
The police discovered that the gang was already infiltrated by an agent.
Security experts warned that the private network had been infiltrated by hackers months before the data leak.
The documentary explores how the activist group became infiltrated by undercover officers, leading to a complete breakdown of trust among its core members.
Often follows a linking verb or appears in passive constructions.
The spy infiltrated into the buildingThe spy infiltrated the buildingWhen used as a verb, 'infiltrate' is transitive and does not require the preposition 'into'.