Wired’s Ryan Singel wrote a great article on the useful exploitation of Radio Intercept of EMI/RFI:
Decades ago the FCC has set standards prohibiting electrical devices from interfering with other ones, concerned merely about noise. These days we know that computer monitors, audio cables and other information machines like credit card machines in restaurants actually emit sensitive information.
Outside of the government, almost nothing was known about how such eavesdropping worked until 1985, when a computer researcher named Wim van Eck published a paper explaining how cheap equipment could be used to pick up and redisplay information from a computer monitor.
Read the whole article at: http://blog.wired.com/27bstroke6/2008/04/nsa-releases-se.html
And as Ryan mentions: ….. how the United States first learned about the fundamental security vulnerability called “compromising emanations” is revealed for the first time in a newly-declassified 1972 paper TEMPEST: A Signal Problem(.pdf), from the National Security Agency’s secret in-house journal Cryptologic Spectrum.
Interesting material – what information does you radio gear give away without you knowing it?