The Washington Post is reporting that the National Security Agency tracks the locations of nearly 5 billion cellphones every day overseas, including those belonging to Americans abroad.
The newspaper says the NSA inadvertently gathers the U.S. location records, along with the billions of other records it collects by tapping into worldwide mobile network cables.
The program is detailed in documents given to the Post by former NSA systems analyst Edward Snowden.
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Such data means the NSA can track the movements of almost any cellphone around the world, in addition to tracking who that cell user is calling.
A spokesman for the Office of the Director of National Intelligence declined to comment on the report.
NSA officials have said no NSA program gathers data on U.S. cellphones inside the U.S.