The keyboard can be modified, for example, with SURLYSPAWN, a 'Keystroke monitor technology that can be used on remote computers that are not internet connected'. It's probably one of the most used NSA devices, being cheap($30) and easily installable.

http://upload.wikimedia.org/wikipedia/commons/f/fc/NSA_SURLY...

http://en.wikipedia.org/wiki/NSA_ANT_catalog