Following on from
Jes5199, this evil
ubercracker technology is, in it's full form,
Transient Electromagnetic Pulse Surveillance Technology, and can be defined as the practice of intercepting and recording data represented in electromagnetic form.
A TEMPEST device can snoop on your computing and networking by reading the electromagnetic emanations of your PC, your phone line if you use a modem, or your LAN cable.
You occasionally see the term TEMPEST shielding in Government informatics.