The NSA inadvertently gathers the location records of "tens of millions of Americans who travel abroad" annually, along with the billions of other records it collects by tapping into worldwide mobile network cables, the newspaper said in a report on its website.

Such data means the NSA can track the movements of almost any cellphone around the world, and map the relationships of the cellphone user. The Post said a powerful analytic computer program called CO-TRAVELER crunches the data of billions of unsuspecting people, building patterns of relationships between them by where their phones go. That can reveal a previously unknown terrorist suspect, in guilt by cellphone-location association, for instance.
http://www.businessweek.com/ap/2013-...llphones-daily