Conficker started spreading last November, and there are many variants of the virus around that can spread in several different ways, including through infected USB drives. If you are worried that your PC might be infected, Microsoft have released a tool capable of removing several Conficker variants, plus several other malware infections. You can download it from here:
Even if you don't think you've got a problem I would recommend downloading and running this and then repeating the scan once every week or two as I've seen several instances of decent anti-virus software being fooled by this.
By the way, this is a typical time for people to send all their friends mail foretelling great disaster and so on. Just remember to check in at snopes.com (link to the virus and hoax page) before taking any notice.