Quick question. Not sure if you guys would know the answer to this, but I just passed through the security checkpoint, and I was told by the TSA that they were going to run tests on my laptop. My question is, what tests were they running exactly.

For explosives. I had something similar done myself earlier this year. They randomly test peoples hardware.

Usually when a screener wants to check a computer, he/she usually swabs the machine one or more times and then put the swab(s) in a device which tests for explosive residues. That is pretty much all there is to it from what I've experienced.