From a discussion about protecting yourself against most ‘black bag’ and ‘evil maid’ attacks.

put distinctive scratches into all your peripherals, take a photo, and regularly check that the scratches are identical to the photo. This is how weapons inspectors ensure the seals protecting weapons caches have not been tampered with. The seals are scratched in a distinctive way that can’t be forged, then check periodically. Use tamper evident tape on your devices to slow down a burglar that wants to plant a keylogger in your keyboard.

The computer in question is an ‘air gapped’ machine, which means it is not connected to any network. You’d use it for extreme operational security (i.e. working with leaked NSA documents).

If you have a desktop [computer], put super glue in all the USB interfaces so they aren’t functional. Do the same to any interface on the mother boards that could attach removable media. Try to make the case impossible to open (bonus points for encasing it in cement except for the fan, CD tray, cables for keyboard/mouse, power cable and power button).

Turns out that really isolating a computer that you work on is a very hard thing to do. The latest threat seems to be some kind of super-malware that can bridge air gaps by communicating via a computer’s built-in speaker and mic. Allegedly it ‘talks’ at around 18kHz which is a frequency most people cannot hear.

a restaurant’s walk-in freezer is the poor man’s faraday cage