The Conficker worm is spreading worldwide, now affecting around 10 million personal and business computers. A report from F-secure says it leaped from 2.4 million to up to 3 times that number in just 3 days. Are you scared yet?
The worm can be acquired through a vulnerability in the Microsoft system which could allow remote code execution if an affected system received a specially crafted RPC request. This is not a problem if you already have the patch they sent out in October.
The worm can also “mutate” and launch “brute force attacks” that relentlessly try thousands of letter and number combinations in codes to steal personal passwords and login information.
Lastly, the worm can infect removable devices and network shares with an autorun file that executes as soon as a USB drive or other infected device is connected to a victim PC. This last one may be most common for personal computers, so protect yourself RIGHT NOW and turn off your AutoRun. I think you can do this by right clicking on the CD-ROM drive or USB drive, choosing the Properties > Autoplay > and the radio button for "Prompt me each time to do an action". But I'm not an expert so if you want more info, try this instead.