Your source?
Communications techs in my highly classified Navy Crypto Communications job.
Alamo-Girl; provided this wiki link:
http://en.wikipedia.org/wiki/ECHELON
There have been abundant souces in the years since—confirming what I was told in my work.
Reportedly, there’s even a machine which can read snail mail without opening it. Plausible. Get the carbon ink atoms to give off a certain wave detectable and unfoldable by computer . . . voila.
And still folks stick their heads in the sand and disbelieve any such. Cosnervative folks who ought to be in the vanguard of preparing, at least. Sigh.