Good reading - an intelligence report from the cold war.
A recently (partially) declassified document on the history of TEMPEST.
Background: TEMPEST is the reconstruction of signals from electronic noise or actual sounds made by that equipment.
Example, you could see anything that was on an old-fashioned computer monitor from a quarter mile away or more, through a brick wall. The trick was to hook up a radio receiver to listen for the signal made by the scan ray tracing over the screen with the right circuitry to transform that back into a TV signal and then run that into your own monitor for viewing.
Hat tip: Schneierblog
Background: TEMPEST is the reconstruction of signals from electronic noise or actual sounds made by that equipment.
Example, you could see anything that was on an old-fashioned computer monitor from a quarter mile away or more, through a brick wall. The trick was to hook up a radio receiver to listen for the signal made by the scan ray tracing over the screen with the right circuitry to transform that back into a TV signal and then run that into your own monitor for viewing.
Hat tip: Schneierblog