The next time these machines are started, the worms become active. Internet worms, depend on e-mail systems to multiply themselves. They arrive as an e-mail attachment which has to be started by a user. When it locates a victim, it copies itself to the new host and then starts the search again. They then infect these machines and may also use e-mail to send themselves to other locations.
Internet Worms are bigger than program viruses and can have more abilities.
Newer worms are able to update themselves from Internet resources. A program that hides its true intention is called a Trojan horse. It was named after the famous hollow wooden horse used by the Greek hero Ulysses to sneak soldiers into the ancient city of Troy. This tactic proved devastating for Troy. Likewise, today's Trojan horses can be dangerous to your computer's software.