a Trojan horse

a Trojan horse

someone or something that attacks the group or organization it belongs to

Usage notes: In Greek stories, the Trojan horse was a large wooden horse that the Greeks used to take soldiers secretly into the city of Troy in order to destroy it.

Traditional Labour supporters have accused the new leadership of being a Trojan horse trying to destroy the party from within.

See work like a dog

See also: horse, Trojan