The nearly 5 billion records collected daily go into a database that stores information about the locations of hundreds of millions of e-devices, allowing the NSA to track individuals' movements and map any potential relationships, top-secret documents offered by former NSA contractor Edward Snowden and intelligence officers indicate.
While the NSA doesn't target Americans' location data deliberately, it acquires a substantial amount of information on the locations of domestic cellphones "incidentally," the Post said in an exclusive story published Thursday.
One senior collection manager told the Post the agency was "getting vast volumes" of location data worldwide by tapping into the cables connecting mobile networks that serve U.S. and foreign cellphones. Data also are often collected from U.S. citizens who travel abroad with their cellphones.
In scale, scope and privacy ramifications, the efforts to collect and analyze location data may be unparalleled among NSA surveillance programs disclosed since June, the Post said.
U.S. officials said the programs were lawful and meant strictly to develop intelligence about foreign targets.
"There is no element of the intelligence community that under any authority is intentionally collecting bulk cellphone location information about cellphones in the United States," Robert Litt, general counsel for the Office of the Director of National Intelligence, which oversees the NSA, told the Post.
The NSA collects locations in bulk because its most powerful analytic tools allow agency analysts to look for unknown associates of known intelligence targets by tracking people whose movements intersect, officials told the Post. What creates issues among privacy advocates is that location data, collected over time, is extremely sensitive.
"One of the key components of location data, and why it's so sensitive, is that the laws of physics don't let you keep it private," Chris Soghoian, principal technologist at the American Civil Liberties Union, told the Post.
While people who value their privacy can encrypt emails and alter online identities, "the only way to hide your location is to disconnect from our modern communication system and live in a cave," Soghoian said.
Three Democratic senators -- Ron Wyden of Oregon, Mark Udall of Colorado and Barbara Mikulski of Maryland -- introduced an amendment to the 2014 defense spending bill that would require U.S. intelligence agencies to state whether they collected or plan to collect location data for "a large number of United States persons with no known connection to suspicious activity."
Senior intelligence officials declined to estimate for the Post the number of Americans whose locations are tracked as part of the NSA's collection of data overseas.
"It's awkward for us to try to provide any specific numbers," one official said in a phone interview. An NSA spokeswoman participating in the call said the agency couldn't calculate such a figure.