-- A Few Things on Van Eck's Method of Eavesdroping --
  Opticon the Disassembled - UPi

 Dr Wim Van Eck, was the  one who  developed the  anonymous method for
eavesdroping  computers  ( and, apparently, not  only ) from  distance,
in  the  laboratories of  Neher, Holland. This  method is  based on the
fact that monitors do transmit electromagnetic radiations. As a device,
it is not too  complex  and it can be  constructed from an  experienced
electronics  phreak. It  uses a simple-direction  antenna  which  grabs
monitor  signals from  about 800 meters away. Simplified schematics are
available from Consumertronics.

 TEMPEST stands for Transient  ElectroMagnetic  Pulse Emanation STandard.
It concerns the quantity of  electromagnetic radiations from monitors and
televisions, although  they  can also  be  detected on  keyboards, wires,
printers and central units. There are some  security levels in which such
radiations are  supposed  to be  untraceable by  Van  Eck  systems. Those
security  levels or  standards, are  described  thoroughly in a technical
exposition  called  NACSIM  5100A, which  has been  characterized by  NSA
classified.

 Variations of the  voltage of the electrical current, cause electromagnetic
pulses in the form of  radio waves. In cathode ray  tube ( C.R.T. ) devices,
such as  televisions and monitors, a source of  electrons scans the internal
surface and activates  phosphore. Whether or not the scanning is interlaced or
non-interlaced, most  monitors  transmit  frequencies  varying from 50 to 75
Mhz per second. They also  transmit harmonic  frequencies, multiplies of the
basic frequencies; for example a transmitter with signal of 10 Mhz per second
will  also  transmit  waves of 20, 30, 40 etc. Mhz. Those  signals are
weaker  because the  transmiter itself  effaces them. Such variations in the
voltage is what the Van Eck system receives and analyzes.

 There are ways to prevent or make it harder for someone to monitor
your  monitor. Obviously  you cannot  place your  computer system
underground and cover it with a  Faraday cage or a  copper shield
( If your case is  already that, then you know more about Van Eck
than I do ). What else ?

 (1) Certain computers, such as Wang's, prevent such divulges;
 give preference to them.

 (2) Place your monitor into a grounded metal box, 1.5 cm thick.

 (3) Trace your tracer(s). They gonna panic.

 (4) Increase of the  brightness and  lowering of the contrast
 reduces TEMPEST's power. Metal objects, like bookshelves,
 around the room, will also help a little bit.

 (5) Make sure that two or more monitors are transmitting at the same
 frequency and let them operate simultaneously; this will confuse
 Van Eck systems.

 (6) Buy or make on your own, a device which will transmit noise
 at your monitor's frequency.

 (7) Act naturally. That is:

 (a) Call IRC, join #hack and never mumble a single word.

 (b) Read only best selling books.

 (c) Watch television at least 8 hours a day.

 (d) Forget altruism; there is only you, yourself
     and your dick/crack.

 (8) Turn the monitor off.