What type of malware disguises itself as legitimate software?

A Trojan horse is a type of malware that masquerades as legitimate software, tricking users into installing it. Unlike traditional viruses and worms that can self-replicate, a Trojan relies on social engineering to entice users into executing it, believing it's a useful or necessary program. Once activated, it can perform various malicious actions, such as stealing data, providing unauthorized access to the system, or downloading additional malware.

In contrast, worms are standalone malicious programs that replicate themselves and spread without any user intervention. Spyware silently collects information about a user’s activities without their consent, and while it can also be disguised, it does not typically present itself as legitimate software to the same extent as a Trojan. Ransomware encrypts a user's data to demand payment for decryption, but again, it does not generally masquerade as something else. Therefore, the defining characteristic of a Trojan horse lies in its ability to deceive users into thinking it’s a trusted application.