NSAは，１日に約５０億件の携帯電話位置情報を収集している

下記の記事が出ている。

　NSA tracking cellphone locations worldwide, Snowden documents show
　Washington Post: December 5, 2013
　http://www.washingtonpost.com/world/national-security/nsa-tracking-cellphone-locations-worldwide-snowden-documents-show/2013/12/04/5492873a-5cf2-11e3-bc56-c6ca94801fac_story.html

　NSA collects nearly 5 billion cellphone location records per day
　ars technica: December 5, 2013
　http://arstechnica.com/tech-policy/2013/12/nsa-collects-nearly-5-billion-cellphone-location-records-per-day/

　NSA 'tracking' hundreds of millions of mobile phones
　BBC: 5 December, 2013
　http://www.bbc.co.uk/news/technology-25231757

　The NSA could figure out how many Americans it’s spying on. It just doesn’t want to.
　Washington Post: December 4, 2013
　http://www.washingtonpost.com/blogs/the-switch/wp/2013/12/04/the-nsa-could-figure-out-how-many-americans-its-spying-on-it-just-doesnt-want-to/

[追記：2013年12月11日]

関連記事を追加する。

　New documents show how the NSA infers relationships based on mobile location data
　Washington: December 10, 2013
　http://www.washingtonpost.com/blogs/the-switch/wp/2013/12/10/new-documents-show-how-the-nsa-infers-relationships-based-on-mobile-location-data/