trojan horse

Noun

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

• a program that appears desirable but actually contains something harmful
  • the contents of a trojan can be a virus or a worm
    
  • when he downloaded the free game it turned out to be a trojan horse
    

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

Related words

• Synonyms: 
  Trojan Horse , Wooden Horse , trojan , fifth column , Trojan horse