I know how the Echelon system works. The name's the giveaway. The text matching system is divided into a number of levels of complexity. Suspect transactions of information are picked up by the first, most simple level of processing which is extremely fast and looks only for single words or something. Then everything picked up by this level is passed onto further, more complex echelons of reviewing either being eliminated or finally passed onto a human user. It makes the most sense. And means the system would be automatically immune to all that jamming crap we were fooling around with years ago.
Course, it'd still be defeated by freely available encryption.