An anglo-saxon surveillance system (USA, Great Britain, Australia, New Zeeland, etc) which trawls through global information sources finding particular things that ain't in the interest of US security (read: US interests, read money, profit and more).
Usually its the writings usually of some small, insignificant minority or obscure individual who unfortunately fits their rather narrow-minded conception of some psychographic profile that they consider to be a 'terrorist'.
In a system that rationalises things in terms of 'individualism' you reify the complexity of a society and to seperate a complex mass into individuals is a process that very much reflects your own interpretive biases and well, you end up strengthening existing stereotypes.
Echelon and others systems like it, provide distinct diplomatic, technical and military advantages. Particularly in regards to economic espionage and the benefits that targetted signals intelligence can bring. Echelon assists most in the export driven industries. Echelon is not about security, it's about instrumental rationality.
Intelligence agencies generally justify this and other national spy projects because of security concerns. These are generally times of panic and are used as excuses to take away a bit of your privacy and civil rights that they want to do anyway.
Jam Echelon Day is futile as the spoofed messages can be indentified and then ignored.
It is likely that there up to 50 different national security systems trying to achieve similar global electronic communications