The National Security Agency trawling program sometimes assumed to be reading the net for the US Government's spooks. Most hackers describe it as a mythical beast, but some believe it actually exists, more aren't sure, and many believe in acting as though it exists just in case. Some netters put loaded phrases like "KGB", "Uzi", "nuclear materials", "Palestine", "cocaine", and "assassination" in their sig blocks to confuse and overload the creature. The GNU version of Emacs actually has a command that randomly inserts a bunch of insidious anarcho-verbiage into your edited text.
There is a mainstream variant of this myth involving a "Trunk Line Monitor", which supposedly used speech recognition to extract words from telephone trunks. This one was making the rounds in the late 1970s, spread by people who had no idea of then-current technology or the storage, signal-processing, or speech recognition needs of such a project. On the basis of mass-storage costs alone it would have been cheaper to hire 50 high-school students and just let them listen in. Speech-recognition technology can't do this job even now (1993), and almost certainly won't in this millennium, either.
The peak of silliness came with a letter to an alternative paper in New Haven, Connecticut, laying out the factoids of this Big Brotherly affair. The letter writer then revealed his actual agenda by offering - at an amazing low price, just this once, we take VISA and MasterCard - a scrambler guaranteed to daunt the Trunk Trawler and presumably allowing the would-be Baader-Meinhof gangs of the world to get on with their business.