Trojan horse
noun [ C ]
ukussomeone or something in a system, organization, etc. that at first seems to be helpful, but then causes harm:
Critics called the 7% cap a Trojan horse for increasing taxes on the working poor.
IT
a type of software, usually downloaded from the internet, that seems to be an ordinary program but that can destroy, or allow someone to steal, data:
Trojan horse program/malware/virus
It's easier than you think to inadvertently download a malicious Trojan horse.