What is the major difference between a worm and a Trojan horse?

A worm is specifically designed to self-replicate and propagate across networks or systems without any user action, whereas a Trojan horse disguises itself as legitimate software to trick users into running it but relies entirely on user execution and does not self-reproduce or spread on its own.

Both worms and Trojan horses are categories of malicious software; a Trojan horse is not a legitimate utility - it merely pretends to be one to deceive the user.

This reverses the facts entirely - worms are malicious self-replicating programs, not anti-virus software, and Trojan horses are malware that masquerades as legitimate applications.

While some worms propagate via email, many exploit network vulnerabilities or removable media; email delivery is not the defining characteristic that distinguishes a worm from a Trojan horse.