A person who enters a place without permission, often with hostile or illegal intent. Can be used for physical intrusion (home, building, territory) or in a broader sense (e.g., computer system).
An intruder broke into the house last night.
警備員が侵入者を見つけた。
The security guard spotted an intruder.
trespasser; intruder
Compound of 侵入 (intrusion) + 者 (person).