What is a Trojan horse in computing?

A Trojan horse in computing refers to a type of malicious software that disguises itself as a legitimate program to deceive users. This misleading representation encourages users to download and execute the software, which can lead to unauthorized access to the system, data theft, or other harmful activities. Unlike viruses or worms, which can self-replicate, Trojan horses rely on the user’s action to spread, often leading to exploitation of the system's vulnerabilities.

The other choices do not fit the definition of a Trojan horse. Antivirus software is meant to detect and remove malware, while secure file transfer methods relate to the protection of data during transmission, and system diagnostic tools are used for troubleshooting and maintaining system health. None of these correctly capture the essence of a Trojan horse as a deceptive program that misrepresents its true intent.