[Senator Bedfellow]

If you have unrestricted physical access, you will inevitably compromise the machine. In a lab environment, you have physical contact with the machine, but it is hardly unrestricted access insofar as someone's likely to notice you rebooting the machine, plugging in your own hardware, or pulling out your screwdrivers and going to work. You should not be able to compromise the machine merely by sitting down and logging in, and that's what happened here.

[Swordmaker]

...someone's likely to notice you rebooting the machine, plugging in your own hardware, or pulling out your screwdrivers and going to work.

Sorry, but you would be surprised at what people DON'T notice or do and assume the person they noticed belonged there. Often audacity will get a criminal more than stealth. If someone looks official, most people will assume they are.