wvmarle:
Quick and easy: MOSFET in the hard disk power line. Switch on the power when the finger print is correct. Not sure though how USB behaves with unpowered peripherals - parasitic powering is a real option.There may also be USB switches out there that can be controlled electronically.
Hmm, that sounds interesting, thanks for the advice. I will look further into it and will let you know if I come across a hurdle.
Thanks again.