TEMPEST is said to stand for 'Telecommunications Electronics Material Protected From Emanating Spurious Transmissions' but I also found; 'Transient Emanations Protected From Emanating Spurious Transmissions', 'Transient Electromagnetic Pulse Emanation Standard', 'Telecommunications Emission Security Standards', and several similar variations on the theme but there is no official meaning for TEMPEST it is more the name of the phenomenon rather than an acronym.
How do these “intelligence-bearing emanations” occur? Basic electromagnetic theory tells us that electromagnetic fields occur as current flows through a conductor. A conductor can be anything metal (your power cord, your CAT5 cable, your phone cord, etc). How does your CAT5 cable pass data? In a simple explanation, current is pushed along the wire and the data goes with it; the more current pushed down the wire and the longer the wire the greater potential for these “emanations” because of growing electromagnetic fields.
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