Firewalls—software solutions that can protect the PCs in your home network against snooping from outside invaders—are supposed to be the stuff of magic. But according to a researcher at the University of California, he's figured out a way to identify computers behind firewalls. UC doctoral student Tadayoshi Kohno uses a technique called digital fingerprinting to uniquely identify PCs protected by firewalls and can track those devices even when they move from access point (AP) to AP behind the firewalls. Most damaging: Physical distance doesn't change the results. The security implications are, of course, huge. But at this point, Kohno's work hasn't been put to evil use. At least not that you're aware of