Beware the RED USB drive
When you work on a secure site the networks are of course air-gapped. So the only form of data transfer for normal PC's* is the RED usb stick... Which has to be signed for and audited in and out.
If you saw a red USB that was not in someones possession, you were not to touch it, you were to ring security immediately who would send armed ninja to appropriately dispose of the USB... and the person who had not looked after it. Security used to leave them on the floor in hallways as a honey-trap for the unwary.
It's not called sneaker-net for nothing!
*Secure Magneto Optical drives (EMP proof) were available for those who could use them!