In addition, because you've directly connected to the attack PC on a peer-to-peer basis, if you've set up your PC to allow file sharing, the attacker can have complete run of your PC, stealing files and data and planting malware on it.

You can't actually see any of this happening, so you'd be none the wiser. The hacker steals what he wants to or plants malware, such as zombie software, then leaves, and you have no way of tracking him down.

All that is bad enough, but it might not be the end of the attack. Depending on how you've connected to that ad hoc network, the next time you turn on your PC, it may automatically broadcast the new "Free Wi-Fi" network ID to the world, and anyone nearby can connect to it in ad hoc peer-to-peer mode without your knowledge -- and can do damage if you've allowed file sharing.

While some of these ad hoc networks advertising themselves as available for connection may be attributable to Windows behavior that the PC's user is unaware of, wireless ad hoc attacks may be more common that you think. Security company Authentium Inc. has found dozens of ad hoc networks in Atlanta's airport, New York's LaGuardia, the West Palm Beach, Fla., airport and Chicago's O'Hare. Internet users have reported finding them at LAX airport in Los Angeles.

Authentium did an in-depth survey of the ad hoc networks found at O'Hare, visiting on three different occasions. It found more than 20 ad hoc networks each time, with 80% of them advertising free Wi-Fi access. The company also found that many of the networks were displaying fake or misleading MAC addresses, a clear sign that they were bent on mischief.