The US National Security Agency has justified tracking the data of millions of people, wherever they are in the world. The NSA says its tracking of cell phones overseas is legally authorized under a presidential order. The intelligence agency says it isn\'t tracking every foreign phone call, and it takes measures to limit how much US data is collected. It was revealed earlier this week that the NSA gathers up to five billion records every day on the location data for hundreds of millions of cell phones worldwide. Documents supplied by whistleblower Edward Snowden detail how the NSA is applying sophisticated mathematical techniques to map cell phone owners\' relationships. Show Less >>