Last month ago I blogged about security researcher Chris Roberts being detained by the FBI after tweeting about avionics security while on a United flight:
But to me, the fascinating part of this story is that a computer was monitoring the Twitter feed and understood the obscure references, alerted a person who figured out who wrote them, researched what flight he was on, and sent an FBI team to the Syracuse airport within a couple of hours. There's some serious surveillance going on.

The link for this article located at Schneier on Security is no longer available.