I'm a TA for an intro to engineering class and one of my students was programming his arduino with his macbook.
He had the gate of an nmos transistor hooked up to pin 11 and the negative end of a 14.4 volt battery hooked up to one of the ground pins. The positive lead of the battery was not attached to anything yet. He also had the arduino plugged in to the usb port of his computer at the time. He says he looked up at the circuit to double check before uploading a new sketch to the board, and when he looked down, his laptop had turned off.
The arduino's ATmega328 was slightly more than warm to the touch and his macbook would not turn back on. The battery on the laptop is fully charged.
My guess is the battery sank -14.8V and fried the arduino and usb port in the process, effectively ruining something on the mobo of the laptop.
Anyone have any ideas before I tell him to buy another arduino, contact apple care, and hope he isn't out a laptop?