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noun

Trojan horse

TROH-juhn HORS
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Trojan horse (noun) means a program that looks harmless or useful but secretly damages a computer or gives an attacker access to it once it is installed. Example: “The free video converter turned out to be a Trojan horse that logged every password he typed.”

noun
1
A program that looks harmless or useful but secretly damages a computer or gives an attacker access to it once it is installed.
"The free video converter turned out to be a Trojan horse that logged every password he typed."
"Most banking Trojan horses arrive as an attachment that the victim opens themselves."
2
A person, thing or plan that hides a harmful purpose behind an attractive or innocent appearance.
"Critics called the tax break a Trojan horse for dismantling the whole welfare system."
"She was accused of being a Trojan horse for her old employer."
3
The huge hollow wooden horse of Greek legend, left outside Troy and taken inside the city by the Trojans, allowing the hidden Greek soldiers to open the gates.
"Virgil's account of the Trojan horse is the most famous version of the story."

How to use Trojan horse

Learner’s notes

In plain EnglishSomething that looks safe but is hiding an attack inside.

When to use it

Neutral in computing; in politics and business it is an accusation and carries a strongly negative tone.

Memory tip

Remember that the danger is invited in. If nobody let it in willingly, it is probably not a Trojan horse.

Trace the full origin ↓
Easily confused with
virus → worm → spyware →
Common pairings
banking Trojan Trojan horse attack a Trojan horse for act as a Trojan horse
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Can you complete this real example?

The free video converter turned out to be a _____ that logged every password he typed.

Etymology

From the Greek legend of the Trojan War, in which Greek soldiers hid inside a large wooden horse to get inside the walls of Troy.

Origin: Greek

Synonyms

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trojan malware backdoor ruse subterfuge ploy wolf in sheep's clothing

Related words

blind trick trap nonsense worm deception malware hoax

Rhymes for Trojan horse

gorse worse Morse Norse horse endorse remorse sawhorse racehorse
See all rhymes for Trojan horse →

Frequently asked questions

What is the difference between a Trojan horse and a virus?
A virus copies itself and spreads from file to file or machine to machine on its own. A Trojan horse does not self-replicate; it relies on the user willingly installing it because it appears to be something desirable. Many real infections combine both behaviours.
Where does the phrase Trojan horse come from?
It comes from the ancient Greek story of the siege of Troy, in which the Greeks pretended to sail away and left a giant wooden horse behind. The Trojans dragged it inside the walls, and the soldiers hidden within opened the gates at night.
Is 'Trojan horse' capitalised?
The first word usually is, because it refers to the city of Troy. In computing, the shortened form is very often written in lower case as 'a trojan'.
What is the meaning of Trojan horse?
"Trojan horse" (noun) means a program that looks harmless or useful but secretly damages a computer or gives an attacker access to it once it is installed.

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