Security watchers are warning of a new worm that's propagating over instant messenger networks run by both AOL and MSN. Nugache-A is also spreading (albeit modestly) as an infected email that uses a variety of well-known Windows exploits to infect vulnerable Windows PCs. If successful, the worm opens a back door that leaves compromised PCs as zombies under the control of hackers. The command and control channel technique used by the worm is unusual. Instead of a static list, the worm connects to infected peers, web security firm Websense reports. The SANS Institute's Internet Storm Centre (ISC) adds that the bots talk to each other via port 8/TCP over an encrypted P2P channel.