I killed one of my laptops when I plugged in a dodgy USB MicroSD card reader. It instantly fried my computer, and I presume it needed a new motherboard after that. It wasn't worth getting it fixed as I only paid about $100 for the laptop.
That's scary. I almost run a USB cord from lappy to lappy before checking if that was ok or not. It was not! so had to cancelled the near fatal result.
I read about such devices ( weapons ? ) last year sometime . There was much emphasis on the "shock-horror" aspect but very little on technical detail. From what I can find right now , it appears to use the power from the USB socket ( 5 Volts @ 500 mA ) to accumulate an electric charge then release it , and continue repeating the process till the machine is toast. Plausible I suppose .... I bet the reader didn't cost anything like the 50 bucks that USB Kill costs , and yet achieved the same result @ EASTER That is a definite no-no , although there are specialized USB leads to to this ( eg for migrating all your stuff to a new machine ) . You may have had a lucky escape there . That few moments spent checking probably saved you much grief ( and money ! )