Trojan horse (computing)

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For the original from Greek mythology, see Trojan Horse.

A trojan horse (often just called trojan) is a kind of malware. It is special computer program that pretends to do a certain thing, but in reality it does something else, such as allow a stranger to access the computer and change it and read its information. In some cases the user notices, in other cases they do not. Spyware programs are examples of programs that work as trojans.

Trojans are generally spread by some form of trickery, for example inducing users to click on bad popups, Email attachments, advertisements, or phony device driver updates. Many trojans act as a backdoor to the computer, contacting a controller which can then have unauthorized access to the affected computer. Trojans may access users' personal information such as banking information, passwords, or personal identity (IP address). It can infect other devices connected to the network. Ransomware attacks are often carried out using a Trojan.

It is rare to get a trojan on your computer by merely visiting a website, though it can happen. Usually, though, trojans are attached to something you download, such as music, wallpapers, backgrounds, games, and especially executable files (.exe) and so on.

It was named after the Trojan Horse in Greek mythology, given as a gift and meant to destroy.