A worm has similar characteristics of a virus. Worms are also self-replicating, but self-replication of a worm is in a different way. Worms are standalone and when it is infected on a computer, it searches for other computers connected through a local area network (LAN) or Internet connection. When a worm finds another computer, it replicates itself to the new computer and continues to search for other computers on the network to replicate.
Due to the nature of replication through the network, a worm normally consumes much system resources including network bandwidth, causing network servers to stop responding.
Different types of Computer Worms are:
• Email Worms: Email Worms spread through infected email messages as an attachment or a link of an infected website.
• Instant Messaging Worms: Instant Messaging Worms spread by sending links to the contact list of instant messaging applications.
• Internet Worms: Internet worm will scan all available network resources using local operating system services and/or scan the Internet for vulnerable machines. If a computer is found vulnerable it will attempt to connect and gain access to them.
• IRC Worms: IRC Worms spread through IRC chat channels, sending infected files or links to infected websites.
• File-sharing Networks Worms:File-sharing Networks Worms place a copy of them in a shared folder and spread via P2P network.