Trojan of or pertaining to ancient Troy.
Trojan Horse in classical Greek mythology, a hollow wooden statue of a horse in which the Greeks are said to have concealed themselves in order to enter and capture Troy; despite the warning of Laocoon, the Trojans breached the city walls to draw the horse inside, so that the Greeks were able the following night to overrun and sack the city.

Trojan Horse in figurative use denotes a person or thing intended secretly to undermine or bring about the downfall of an enemy or opponent; in computing, it is a program designed to breach the security of a computer system while ostensibly performing some innocuous function.
Trojan War the legendary ten-year siege of Troy by a coalition of Greeks led by Agamemnon, described in Homer's Iliad. The Greeks were attempting to recover Helen, wife of Menelaus, who had been abducted by the Trojan prince Paris. The war ended with the capture of the city by a trick: the Greeks ostensibly ended the siege but left behind a group of men concealed in a hollow wooden horse (the Trojan Horse).

Tro·jan Horse • n. Greek Mythol. a hollow wooden statue of a horse in which the Greeks concealed themselves in order to enter Troy. ∎  (also Trojan horse) fig. a person or thing intended secretly to undermine or bring about the downfall of an enemy or opponent: the rebels may use this peace accord as a Trojan horse to try and take over. ∎  (also Trojan horse) Comput. a program designed to breach the security of a computer system while ostensibly performing some innocuous function.

Trojan horse (trojan) An apparently innocent program designed to circumvent the security features of a system. The usual method of introducing a Trojan horse is by donating a program, or part of a program, to a user of the system whose security is to be breached. The donated code will ostensibly perform a useful function; the recipient will be unaware that the code has other effects, such as writing a copy of his or her username and password into a file whose existence is known only to the donor, and from which the donor will subsequently collect whatever data has been written.

Trojan horses can be particularly effective when offered to systems staff who can run code in highly privileged modes. Two remedies are effective: no code should be run unless its provenance is absolutely certain; no code should be run with a higher level of privilege than is absolutely essential. See also virus.

Tro·jan / ˈtrōjən/ • adj. of or relating to ancient Troy in Asia Minor: Trojan legends.• n. a native or inhabitant of ancient Troy.PHRASES: work like a Trojan (or Trojans) work extremely hard.

Trojan Horse Colossal, hollow wooden horse built by the Greeks in the final days of the siege of Troy. Thinking it was a peace offering, the Trojans dragged the horse through the gates, and in the night Greek soldiers who had been hiding within, emerged and opened the city gates to their army.