After this, you may want to be extra careful about plugging in strange USB devices. A researcher calling himself Dark Purple announced a proof-of-concept USB device that, once plugged in, pumps enough electrical current into a computer to shut it down or destroy it completely. It's not a sophisticated attack, but for exactly that reason, it's also very difficult to protect against. In essence, Dark Purple has disguised a stun gun as a USB drive, and since the USB drive can't work without conducting electricity, it's likely to stay vulnerable for quite some time.
Purple describes the device as a repeating loop of electrical surges:
When we connect it up to the USB port, an inverting DC/DC converter runs and charges capacitors to -110V. When the voltage is reached, the DC/DC is switched off. At the same time, the filed transistor opens. It is used to apply the -110V to signal lines of the USB interface. When the voltage on capacitors increases to -7V, the transistor closes and the DC/DC starts. The loop runs till everything possible is broken down.Dark Purple didn't open-source plans for the device, but it's plausible a dedicated hacker could reverse-engineer it from the current description. Because of the direct attack vector and lack of payoff, it's unlikely to be a problem on a broader scale. Still, it's one more reason to be suspicious of mysterious flash drives.
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