trojan

trojan — noun

1. a person who manages to become a member of a team, company, or community and the

1.nounC1
Definition

a person who manages to become a member of a team, company, or community and then secretly works against it, often by leaking information to an opposing side

Example

The police discovered that a trojan had been working inside the protest group for two years.

working inside a group as a secret agent

Roya suspected there was a trojan in the department who was leaking information to a rival company.

Common collocations
  • discover a trojan
  • plant a trojan
  • act as a trojan
  • expose a trojan
Synonyms
  • mole

    stronger implication of deep, long-term cover within intelligence agencies

  • infiltrator

    more general term; a trojan is a type of infiltrator with intent to harm

  • saboteur

    focuses on causing damage, not necessarily on espionage

Antonyms
  • ally

    a trojan works against a group; an ally supports it

Grammar Patterns

trojan + verb (singular/plural)

Usage Note

Frequently used in the context of espionage, corporate intelligence, or political infiltration. The person being referred to is usually already inside the target group before they begin their harmful activity.

Common Mistakes

The spy was a trojan who never entered the building.
The spy was a trojan who had been working in the office for months.
A trojan must already be inside the group or organization.

2. a type of harmful software designed to look like a normal or useful program whil

2.nounB2
Definition

a type of harmful software designed to look like a normal or useful program while secretly damaging computers, stealing data, or granting remote access to attackers

Example

Christopher's laptop slowed down after he accidentally downloaded a trojan disguised as a free music player.

accidentally download a trojan disguised as

The trojan gave the hackers remote control over thousands of home computers around the world.

Common collocations
  • download a trojan
  • detect a trojan
  • remove a trojan
  • trojan attack
  • trojan program
Synonyms
  • malware

    broader category that includes trojans, viruses, worms, and ransomware

  • backdoor

    a type of trojan that gives attackers secret access to a system

Grammar Patterns

trojan + verb (singular)

Usage Note

Unlike a computer virus, a trojan does not spread by copying itself — it relies on users downloading and running the program willingly, often because it looks like legitimate software.

Common Mistakes

The trojan spread to all computers on the network by itself.
The trojan spread because users on the network each opened the infected attachment.
A trojan cannot replicate itself; it needs user action to activate.

3. a native or resident of Troy, the ancient city located in what is now northweste

3.nounB2
Definition

a native or resident of Troy, the ancient city located in what is now northwestern Turkey, especially from the time of the Trojan War described in Greek legends

Example

The ancient Trojans built strong stone walls around their city to protect it from attackers.

Historians believe the Trojans were skilled traders who controlled important sea routes between Europe and Asia.

Trojans as historical people — skilled traders

Common collocations
  • ancient Trojans
  • Trojan people
  • Trojan warriors
  • Trojan legend
Antonyms
  • Greek

    the Trojans fought against the Greeks in the Trojan War

Idioms

work like a Trojan

idiom

To put a lot of effort into your work.

Maya worked like a Trojan to finish the report on time.

Did you see how hard Diego worked like a Trojan yesterday?

trojan — adjective

Word family

Synonym discussion

Sense: noun/1

All four words describe someone who works secretly against a group, but they differ in scope and connotation. A trojan specifically implies that the person has already gained membership or employment inside the target group before acting against it, much like the wooden horse that was taken inside Troy's walls. A mole suggests an agent who has spent years building deep cover, especially within an intelligence agency or government — the focus is on long-term concealment rather than the act of betrayal. An infiltrator is more general: anyone who enters a group dishonestly, whether from outside or already inside. A saboteur focuses on the act of damaging equipment, processes, or morale, without necessarily implying espionage or information theft. A spy emphasises the gathering of secret information, often but not always from an inside position. For example, a trojan would leak internal plans to a competitor; a mole would pass classified files to a foreign government over many years; a saboteur would delete critical data; a spy would photograph confidential documents during a meeting.

mole ↗infiltratorsaboteurspy ↗

Common collocations

Phrases

  • act as a trojan
  • plant a trojan
  • detect a trojan
  • remove a trojan

Etymology

GreekLatinEnglish

The word 'Trojan' comes from Latin 'Troianus', meaning 'of Troy', which itself comes from the Greek 'Trōia' (Τροία), the name of the ancient city in northwestern Asia Minor. The computing sense of 'Trojan' (or 'Trojan horse') dates to the early 1970s, drawing a direct analogy to the story from Homer's Iliad, in which Greek soldiers hid inside a large wooden horse to enter and capture the city of Troy. By the 1980s, 'Trojan' was being used more broadly to describe any person or thing that infiltrates a group by first appearing harmless.