The vast number of ways two or more indiviudals can communicate via the intertubes is mind boggling. For a start you've got 62000+ ports to communicate on. Then you have two primary kinds of packet. Then you have three different kinds of communication (video, audio or plain text). Then you've got numerous forms of encryption.
Simply put - if a terrorist cell wanted to communicate safely it wouldn't take a rocket scientist. Just a disillusioned programmer.
But then, if the security forces stopped looking for magic wands and trying to collect terabytes of useless data they'd have more time for more effective measures. Maybe they'd be able to make their own secure communication network... Now there's a thought.
Reason most large attacks are missed is two fold, number one - there is so much information gathered using drag net techniques it is impossible to differentiate between the legitmate and the fantasy, and number two - as odd as terrorists may be, they're rarely stupid (not the ones that pull off succesful operations). Stupid terrorists tend to come up with plans that don't work and weapons that fail to function. Like trying to set propane cans alight.
At the end of the day, it's down to luck, and convincing most people that we arn't out to screw them over...
These people arn't supposed to be looking after you or wife or your kids, they're supposed to be protecting our way of life, and that, they are failing miserably at as we decend ever further into totaltarian fascism.
But whatever, mines the one with the work visa to a decent country in it.