Neal Stephenson explains this pretty well in "Cryptonomicon" as a method of shutting down all the computers in an N-block radius during an NSA raid.
You should read it if you haven't already.
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Overhead, the Albatross hangs motionless upon the air,
And deep beneath the rolling waves,
In labyrinths of Coral Caves,
The Echo of a distant time
Comes willowing across the sand;
And everthing is Green and Submarine
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