My hypothesis is that science will someday be able to identify sociopaths and terrorists by their patterns of Facebook and Internet use. I'll bet normal people interact with Facebook in ways that sociopaths and terrorists couldn't duplicate.
Anyone can post fake photos and acquire lots of friends who are actually acquaintances. But I'll bet there are so many patterns and tendencies of "normal" use on Facebook that a terrorist wouldn't be able to successfully fake it.
The main reason you can't fake Facebook use patterns is that you can't control how others respond to you. Good friends respond entirely differently than acquaintances, both in quantity and content. I think that sort of difference would show up.
Years ago, during my banking career, a coworker developed a program that looked through bank records for patterns suggesting possible fraud. It worked well enough that he formed his own company, sold the program to banks, and became a wealthy man. The key to the program's success is that crooks don't know there is a normal pattern and so they don't know when they violate it. I think the same would be true for Facebook. There must be dozens of normal Facebook patterns that sociopaths and terrorists wouldn't know about, and therefore couldn't fake.
I imagine that Internet usage patterns could tell experts as much about your brain as an MRI. To put it in simpler terms, if you tell me which web pages you browsed this week, I can come up with a good estimate of your odds of being a terrorist.
Do you think the government is already monitoring your Internet use pattern, if not the specific pages? If not, they will.