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

A worm is a form of malicious program, while a Trojan horse is a utility.

A Trojan horse is a malicious program, while a worm is an anti-virus software.

A worm is self replicating, while a Trojan horse is not.

A worm spreads via e-mail, while a Trojan horse does not.