Autorun worms are malicious programs that take advantage of the Windows Autorun feature. They execute automatically when the device on which they are stored is plugged into a computer.
Autorun worms are commonly distributed on USB drives.
Hairy-A is an example. It exploited the hype around the launch of the final Harry Potter novel. The worm, distributed on USB drives, was hidden in a file that posed as a copy of the novel and automatically infected computers as soon as the USB was plugged in.
AutoPlay is a similar technology to Autorun. It is initiated on removable media prompting users to choose to listen to music with the default media player, or to open the disk in Windows Explorer. Attackers have similarly exploited AutoPlay, most famously via the Conficker worm