The way I like to look at things is like this. You didn't know about the stealth bomber until years after, not everything is kept public. I'm sure they can crack ziplip in seconds.
if they fbi intercepts your personal mail without a warrant, they will know it .... but it will be supressed in court and the case will be dismissed .... assuming you get a non public defender you are safe.
Weeman - the thing you are thinking about it called Tempest. It is based on a phenomena called "VanEck" (sp?) radiated energy (after the guy who wrote a paper on it in the 70's I think). Works on an amazing amount of equipment. Google on Tempest and vaneck or tempest and computer and see what comes up .
So, with all these govt branches watching us and Carnivore sifting through and decoding all our emails, why aren't the World Trade Center Towers still standing?