Hey, all you hotshots who love to spoof your WiFi MAC address just to drive your network admins up the wall -- your days are numbered. (Quick refresher: a MAC address is a unique digital string of numbers and letters attached to every network device, and it never changes when you change networks, unlike an IP address. It's often used for extra security in networks to only allow certain Ethernet/WiFi cards -- but this signature can be pretty easily faked.) And if you're already drafting ways to defat this technique, you may want to consult with Dr. Jeyanthi Hall, of Carelton University in Ottawa, who discovered that every wireless device produced has a unique signal fingerprint determined at the time of production. She analyzed radio signals from 15 devices between six different manufacturers and was able to correctly identify 95 percent of the "transceiverprints," with zero false positives. Maybe Dr. Hall should collaborate with that leather hat hacker guy who built the ultimate WiFi hacking box -- then they'd really have a product the US Government would be interested in.