In an anonymous industrial park in Virginia, in an unassuming brick building, the CIA is following up to five million tweets a day. At the agency's Open Source Center in McLean, a team known affectionately as the 'vengeful librarians' also pores over Facebook, newspapers, TV news channels, local radio stations, Internet chat rooms – anything overseas that anyone can access and contribute to openly. From Arabic to Mandarin Chinese, from an angry tweet to a thoughtful blog, the analysts gather the information, often in native tongue. Keeping track: The CIA team follow up to five million tweets a day around...