You probably know by now that plugging a random USB into your PC is the digital equivalent of swallowing a pill handed to you by a stranger on the New York subway. But serial hacker Samy Kamkar's latest invention may make you think of your computer's USB ports themselves as unpatchable vulnerabilities—ones that open your network to any hacker who can get momentary access to them, even when your computer is locked.

Today Kamkar released the schematics and code for a proof-of-concept device he calls PoisonTap: a tiny USB dongle that, whether plugged into a locked or unlocked PC, installs a set of web-based backdoors that in many cases allow an attacker to gain access to the victim's online accounts, corporate intranet sites, or even their router. Instead of exploiting any glaring security flaw in a single piece of software, PoisonTap pulls off its attack through a series of more subtle design issues that are present in virtually every operating system and web browser, making the attack that much harder to protect against.