The principal of the TEMPEST attack is deceptively simple. Any machine that processes information -- be it a photocopier, an electric typewriter or a laptop -- have parts inside that emit electromagnetic and acoustic energy that radiates out, as if they were tiny radio stations. The waves can even be picked up and amplified by nearby power lines, telephone cables and even water pipes, carrying them even further. A sophisticated attacker can capture the right frequency, analyze the data for patterns and recover the raw information the devices were processing or even the private encryption keys inside the machine.