I know very little about the technical details...
But, one thing that I know is that, this is something about which (still
today) all the secret services are worried about. And about which (still
today) many governmental departments take counter-measures against.
Reading on the Internet, I can find statements like:
"all information processing machines send their secrets into the
electromagnetic ether."
--- http://www.wired.com/threatlevel/2008/04/nsa-releases-se/
"Computers, PC screens and even data lines emit electromagnetic radiation. At
a certain range from the emitting source, it is quite easy receiving and
decoding this radiation and to re-construct its information."
---
http://www.faradaycages.com/index2.php?p=Content&id=129&nav=Eavesdropping&nav_grp=Espionage
And, concerning LCD monitors, specifically, I can find, for example, this
information:
http://www.dslreports.com/forum/r27848275-TEMPEST-Attacks-LCD-Monitor-leaks-system-noise-to-FRS
For everyone who wants to make a (funny) test, using a Free Software program
to that effect, here goes this link: http://www.erikyyy.de/tempest/
And here goes a video demonstration of such program in action, on an LCD
monitor: http://www.youtube.com/watch?v=oLQbp6hj7-c
