a program that appears desirable but actually contains something harmful
"the contents of a trojan can be a virus or a worm"
"when he downloaded the free game it turned out to be a trojan horse"
A native or inhabitant of the ancient city of Troy.
"The security team discovered that the trojan disguised itself as a system update but secretly stole all passwords from the infected computers."
Malware that appears to perform or actually performs a desired task for a user while performing a harmful task without the user's knowledge or consent.
In plain English: A trojan is a type of computer program that looks harmless but secretly steals your information when you run it.
"The computer was infected by an online trojan that stole all my passwords."
Usage: Use "trojan" as a noun to describe malicious software disguised as legitimate programs, but avoid using it for any horse-related idioms like the Trojan Horse story. When referring to celestial bodies that share an orbit with another planet or moon, specify this context clearly since the term is now primarily associated with cybersecurity threats in everyday language.
To infect (a system) with a trojan.
"The hacker managed to infect the entire network by tricking users into downloading what they thought was a legitimate software update, effectively installing a trojan on every machine."
In plain English: To trojan means to secretly get inside something without permission and then cause damage from within.
"The hackers managed to trojanize the software by hiding malware inside its update files."
Of, or relating to, the famed city of Troy or its inhabitants.
"The small asteroid functions as a trojan by sharing Jupiter's stable orbital path around the Sun."
Describing a satellite (moon or minor planet) that shares an orbit with another
In plain English: A trojan is something that looks harmless but actually hides dangerous code inside it to trick you into letting it onto your computer.
"The computer security experts warned that downloading files from unknown websites could install a trojan virus on your device."
The word comes from the story of the Trojan Horse and originally referred to anything related to Troy or its people. In modern English, it specifically describes a deceptive program that hides malicious code inside seemingly harmless software.