ˌTrojan ˈHorse noun

1. the Trojan Horse a wooden horse used by Greek soldiers to trick their enemies the Trojans during the Trojan War. The Greeks hid inside a large wooden model of a horse and were taken into Troy by Trojan soldiers, who thought that it was a gift.

2. someone or something that is accepted because it seems good or harmless, but that is really intended to cause harm:
Senator Simon claimed the new law would reduce violence on TV, but opponents have attacked it as being a ‘Trojan Horse’ that would lead to censorship of TV programming.

[TahlilGaran] Dictionary of Contemporary English ▲

a Trojan horse
someone or something that attacks the group or organization it belongs to.
Traditional Labour supporters have accused the new leadership of being a Trojan horse trying to destroy the party from within.

[TahlilGaran] English Idioms Dictionary ▲