General intruder:
* Infiltrateur: This translates to "infiltrator" and implies someone who enters a place or group secretly, often with malicious intent.
* Indésirable: This means "undesirable" and refers to someone who is not welcome.
* Personne non autorisée: This literally translates to "unauthorized person" and implies someone who is not supposed to be in a certain place.
Specific types of intruders:
* Cambrioleur: This refers to a burglar or thief who enters a building to steal something.
* Pirate informatique: This refers to a hacker who illegally accesses computer systems.
* Envahisseur: This translates to "invader" and refers to someone who enters a place or country by force.
The best translation will depend on the specific situation and the type of intrusion you are referring to.