A subversive group that supports the enemy and engages in espionage or sabotage; an enemy in your midst.

synonym: fifth column.

Dutch: vijfde colonne

A program that appears desirable but actually contains something harmful:
— When he downloaded the free game it turned out to be a trojan horse.

synonym: trojan.

Dutch: Trojaan
Polish: trojan, koń trojański

A large hollow wooden figure of a horse (filled with Greek soldiers) left by the Greeks outside Troy during the Trojan War.

synonym: Wooden Horse.