Source: Wikipedia (TEMPEST Page found here)
The term TEMPEST is often used broadly for the entire field of Emission Security or Emanations Security (EMSEC). The term TEMPEST was coined in the late 60's and early 70's as a codename for the NSA operation to secure electronic communications equipment from potential eavesdroppers as well as provide the ability to intercept and interpret those signals from other sources.
Compromising emanations consist of electrical or acoustical energy intentionally or by mishap unintentionally emitted by any number of sources within equipment/systems which process national security information. This energy may relate to the original encrypted message, or information being processed, in such a way that it can lead to recovery of the plaintext. Laboratory and field tests have established that such CE can be propagated through space and along nearby conductors. The interception/propagation ranges and analysis of such emanations are affected by a variety of factors, e.g., the functional design of the information processing equipment; system/equipment installation; and, environmental conditions related to physical security and ambient noise. The term "compromising emanations" rather than "radiation" is used because the compromising signals can, and do, exist in several forms such as magnetic- and/or electric-field radiation, line conduction, or acoustic emissions.
MaxVision's engineers have a wide range of experience designing TEMPEST class products for previous companies that sold into the government markets in the 1980's. MaxVision is currently developing a new generation of TEMPEST class rugged portable products. If you have unique TEMPEST requirements for rugged computers, please contact MaxVision for more information.