The world of computing is full of jokes and myths, but on the other side, electronics has a very particular ability to turn those myths into reality. More than once I heard about computers ruined by an electric lighter that discharges its spark into a USB port, though I never witnessed such a thing. However, a Russian blog published last February the design of a USB drive that can literally destroy a computer…
The story begins with a quote extracted from a Skype chat. That quote describes a stolen USB drive from a backpack on the subway, which was marked with the number "128". The thief connected the drive and burned half of his laptop. Immediately after, he wrote "129" on the drive and placed it in the outer pocket of his backpack, an easy prey for anyone who wants to steal it…
True? A hoax? We will probably never know, but the question stuck in the minds of some engineers. Is it possible to build a computer-killing USB drive? The author of the original article, known as Dark Purple, was about to order some PCBs for other projects and decided to experiment a little. The USB interface has electrostatic protection diodes, filters, and other additional elements with safety in mind. The “physical administration” (so to speak) of USB ports is integrated (at least a good part of it) in the processor, while in older systems, the job is handled by the famous northbridge and southbridge, with some variations depending on each model and design adopted by the manufacturer. "Destroying" a computer means putting an end to that whole structure, and at least burning the port.
In just one week, Dark Purple prepared a prototype, ordered the PCBs from China (apparently of terrible quality), hand-soldered each component, and covered the circuit with the casing of a traditional USB drive. To bring this monstrosity to life, he used a “DC-DC inverter converter”, prepared in such a way that when connected to a computer's USB port, it proceeds to charge the internal capacitors to -110 volts (yes, that's negative). When it reaches the desired voltage, the converter turns off, and at the same time a transistor opens, unleashing those -110 volts on the USB interface lines. Once the capacitor voltage drops to -7 volts, the converter activates again, repeating the cycle until everything is ruined. A fried computer, please don't forget the fries.
Just one more case where reality surpasses fiction. The story of the numbered drive may be nothing more than that, but the point is that someone needed only a week to put that crazy theory into practice. USB ports not only have the potential to easily allow infections, but they also lack a solid defense (even with advanced protections, the port probably won't work anymore) against such an aberrant attack. Needless to say, anyone who sees a USB drive on the street would do well to leave it there. Are we facing the "21st century" version of the famous floppy bomb?
