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Old English Troian "of or pertaining to ancient Troy," from Latin Trojanus, from Troia, Troja "Troy," from Greek Tros, name of a king of Phrygia, the mythical founder of Troy. In 17c., it was a colloquial term for "person of dissolute life, carousing companion." The trade name for a brand of prophylactic contraceptive was registered 1927 in U.S. Trojan horse is attested from 1570s; the computer virus sense is attested by 1982.