Ok prepare to strap that tinfoil hat on two notches below excruciating, we’re going to talk about TEMPEST. What is TEMPEST?  It’s defined in NSTISSI-7000 as:

Electronic and electromechanical information-processing equipment can produce unintentional intelligence-bearing emanations, commonly known as TEMPEST. If intercepted and analyzed, these emanations may disclose information transmitted, received, handled, or otherwise processed by the equipment. (1)

and in NSTISSI 7003 (TEMPEST GLOSSARY) as:

“A short name referring to investigations and studies of compromising emanations. It is often used synonymously for the term "compromising emanations"; e.g., TEMPEST tests, TEMPEST inspections.” (2)

Compromising Emanations (CE) are defined as:

“Unintentional intelligence-bearing signals, which, if intercepted and analyzed, disclose the national security information transmitted, received, handled or otherwise processed by any information-processing equipment.” (3)

Clear as mud?  What this means is that your computer, your computer monitor, your CAT5 cable going into your router from your computer, your coax cable into your cable modem, and even your power cord going into the wall can carry electronic and electromechanical signals distances away from your computer and could possibly be intercepted either off the wires or through the air.  Ok, maybe one more notch on that hat.

Image at top of document with Rory Culkin, Mel Gibson and Abigail Breslin from the movie Signs (2002). © Touchstone Pictures. All rights reserved.