A two-year old authentication bypass technique that received wide attention earlier this week as a means to get around Windows XP password protection also works on Windows Vista, a report released on Wednesday reveals.

On Monday, New Zealand-based security researcher Adam Boileau released "winlockpwn," software for bypassing Windows XP SP2 authentication using a Linux PC connected via FireWire to a target Windows PC. He also explained that the technique works against computers running Linux, Mac OS X, and BSD Unix.

On his Web site, Boileau said Microsoft doesn't consider the attack a legitimate security vulnerability. Indeed, as Microsoft points out in the third of its 10 Immutable Laws of Security, "If a bad guy has unrestricted physical access to your computer, it's not your computer anymore."

Two weeks ago, researchers from Princeton University, the Electronic Frontier Foundation, and Wind River Systems reaffirmed this proposition when they released details about how encryption keys for disk-based encryption systems could be recovered more easily by chilling a computer's memory chips.

Peter Panholzer of SEC Consult Vulnerability Lab, based in Vienna, Austria, said in a paper released on Wednesday that his company has demonstrated a proof-of-concept attack on Windows Vista using its own Vista unlock tool.

"In short, our Vista unlock tool uses signature matching to find the respective binary code in the target node's memory (the same method is used in winlockpwn)," Panholzer explained. "The process of searching the pattern and manipulating the DLL code in memory takes a few seconds up to a few minutes. After the patch has been applied, any username and password can be specified at the login prompt for a successful login."

Panholzer doubts Microsoft will address the issue of FireWire authentication bypass because it's not technically a vulnerability; rather he said it's the way the protocol is designed.

"The only known effective way of protecting against the FireWire attack is to deactivate all FireWire and PC Card ports in the device manager," he said.