What is a worm?
A wormis a program that is designed to replicate and spread throughout a computer system automatically , it has the capability to travel without any help from a person. It will usually hide within files and distribute those files through any available network connections.
The biggest danger with a worm is its capability to replicate itself on your system, so rather than your computer sending out a single worm, it could send out hundreds or thousands of copies of itself, creating a huge devastating effect. For example, a worm could send out copies of itself to everyone listed in your e-mail address book, and their computers would then do the same, which causes a domino effect of heavy network traffic that can slow down business networks and the Internet as a whole. When new worms are unleashed, they spread very quickly. They clog networks and possibly cause a long wait for you (and everyone else) to view Web pages on the Internet.
Worms are often used to drain computer resources such as memory and network access, simply by replicating on a large scale. In addition, worms sometimes delete data and spread rapidly via e-mail.
A worm called Code Red made huge headlines in 2001. This worm could clog the Internet so effectively that things would completely grind to a halt. The Blaster Worm has been designed to tunnel into your system and allow malicious users to control your computer remotely.
A worm usually exploits some sort of security hole in a piece of software or the operating system. For example, the Slammer worm (which caused mayhem in January 2003) exploited a hole in Microsoft's SQL server. A worm called Storm, which showed up in 2007, immediately started making a name for itself. Storm uses social engineering techniques to trick users into loading the worm on their computers.