Fuller said the combination worked on all versions of Windows and even on El Capitan, though he still needs to check whether his Mac experiment was a fluke. He also said that the hack was so easy to pull off, he "tested it so many ways to confirm" since he had such a hard time believing it was possible.

He captured the process on cam, which you can watch below, and explained how it works in an email to Ars Technica:

"What is happening in the video, is the USB Armory is being plugged into a locked (but logged in) system. It boots up via the USB power, and starts up a DHCP server, and Responder. While it's doing this, the victim is recognizing it as a Ethernet adapter. The victim then makes route decisions and starts sending the traffic it was already creating to the Armory instead of the "real" network connection. Responder does its job and responds to all kinds of services asking for authentication, and since most OSs treat their local network as "trusted" it sees the authentication request and automatically authenticates. Seeing that the database of Responder has been modified the Armory shuts down (LED goes solid)."

Of course, this is a non-issue if you exclusively use your computer at home, and there's nobody living there you don't trust. But if you tend to bring laptops to coffee shops and other places, check out this prevention technique Fuller recommends, or just make sure you never leave your computer unattended.