Surveillance has foiled '50 terror plots', US spy chief says

America’s sweeping surveillance programmes have foiled 50 terrorist plots worldwide, including one directed at the New York Stock Exchange, according to the director of the National Security Agency.

General Keith Alexander said the two recently disclosed operations – one that gatherscUS phone records and another that is designed to track the use of US-based internet servers by foreigners with possible links to terrorism – are critical in the terrorism fight.