Many computer systems use protective mechanisms, which are mathematically secure but physically vulnerable. In this talk, I will survey the development of such side channel attacks since the late 1990's, and describe various examples of devastating attacks on widely deployed systems. In the last part of the talk, I will describe some recently developed (and previously unpublished) techniques which can be used by an outside attacker to establish long range (>1 kilometer) bidirectional communication with a top-secret computer system which contains only standard untampered hardware components, is completely air gapped, and is perfectly shielded from TEMPEST attacks.