Physical access is pretty much always game over, apart from the iPhone there are not many devices that can stand up to attack. Intel seem to want to make physical access even easier and are now offering JTAG access on USB.
JTAG is a hardware debugging protocol normally seen on embedded systems or accessed through a special adapter on the motherboard. You can use JTAG to pause a processor, step through the instructions being executed and read into memory. With JTAG access you have full access to the machine.
Reading: Babylon's Ashes
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