Trojan horse
/ˌtroʊdʒən ˈhɔːrs/
something that appears benign but contains hidden danger
Trojan horse in a sentence
“The free software was a Trojan horse for malware.”
Origin of Trojan horse
From the wooden horse Greeks used to infiltrate Troy
What does Trojan horse really mean?
A Trojan horse is a threat dressed as a gift — anything welcomed inside the gates because it looks harmless or attractive, only to reveal its true purpose once admitted. The phrase carries a double warning: about deception, and about the eagerness of the deceived to believe.
The story behind Trojan horse
From the Greek legend of the Trojan War: after ten years of siege, the Greeks built a giant wooden horse, hid soldiers inside, and sailed away. The Trojans hauled the "offering" into their city; that night the hidden Greeks opened the gates. Virgil's Aeneid gave the story its enduring line — timeo Danaos et dona ferentes, "I fear the Greeks even bearing gifts." Computer security borrowed the name in the 1970s for malware disguised as legitimate software.
How to use Trojan horse
Use it for anything smuggled in under friendly cover: a contract clause, a political amendment, a "free" app that harvests data. Both noun and modifier work: "the provision was a Trojan horse for deregulation."