Only real defense for billions of devices is physically capping ports.
Last year we wrote about the “USB Killer”—a DIY USB stick that fried almost everything (laptops, smartphones, consoles, cars) that it was plugged into. Now the USB Killer has been mass produced—you can buy it online for about £50/$50. Now everyone can destroy just about every computer that has a USB port. Hooray.
The commercialised USB Killer looks like a fairly humdrum memory stick. You can even purchase a “Test Shield” for £15/$15, which lets you try out the kill stick—watch the spark of electricity arc between the two wires!—without actually frying the target device, though I’m not sure why you would want to spend £65 to do that. The website proudly states that the USB Killer is CE approved, meaning it has passed a number of EU electrical .
The USB Killer is shockingly simple in its operation. As soon as you plug it in, a DC-to-DC converter starts drawing power from the host system and storing electricity in its bank of capacitors (the square-shaped components). When the capacitors reach a potential of -220V, the device dumps all of that electricity into the USB data lines, most likely frying whatever is on the other end. If the host doesn’t just roll over and die, the USB stick does the charge-discharge process again and again until it sizzles.