The National Security Agency is gathering nearly five billion records a day on the whereabouts of cellphones around the world, according to top-secret documents and interviews with U.S. intelligence officials, enabling the agency to track the movements of individuals - and map their relationships - in ways that would have been previously unimaginable.
The records feed a vast database that stores information about the locations of at least hundreds of millions of devices, according to the officials and the documents, which were provided by former NSA contractor Edward Snowden. New projects created to analyze the data have provided the intelligence community with what amounts to a mass surveillance tool.
The NSA does not target Americans' location data by design, but the agency acquires a substantial amount of information on the whereabouts of domestic cellphones "incidentally," a legal term that connotes a foreseeable but not deliberate result.
One senior collection manager, speaking on condition of anonymity but with permission from the NSA, said "we are getting vast volumes" of location data from around the world by tapping into the cables that connect mobile networks globally and that serve U.S. cellphones as well as foreign ones. Additionally, data are often collected from the tens of millions of Americans who travel abroad with their cellphones every year.
In scale, scope, and potential impact on privacy, the efforts to collect and analyze location data may be unsurpassed among the NSA surveillance programs that have been disclosed since June. Analysts can find cellphones anywhere in the world, retrace their movements, and expose hidden relationships among individuals using them.
U.S. officials said the programs that collect and analyze location data are lawful and intended strictly to develop intelligence about foreign targets.
Robert Litt, general counsel for the Office of the Director of National Intelligence, which oversees the NSA, said, "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."
The NSA has no reason to suspect that the movements of the overwhelming majority of cellphone users would be relevant to national security. Rather, it collects locations in bulk because its most powerful analytic tools - known collectively as CO-TRAVELER - allow it to look for unknown associates of known intelligence targets by tracking people whose movements intersect.
Still, location data, especially when aggregated over time, are widely regarded among privacy advocates as uniquely sensitive. Sophisticated mathematical techniques enable NSA analysts to map cellphone owners' relationships by correlating their patterns of movement over time with thousands or millions of other phone users who cross their paths. Cellphones broadcast their locations even when they are not being used to place a call or send a text.
CO-TRAVELER and related tools require the methodical collection and storage of location data on what amounts to a planetary scale. The government is tracking people from afar into confidential business meetings or personal visits to medical facilities, hotel rooms, private homes, and other traditionally protected spaces.
"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," said Chris Soghoian, principal technologist at the American Civil Liberties Union. People who value their privacy can encrypt their e-mails and disguise their online identities, but "the only way to hide your location is to disconnect from our modern communication system and live in a cave."
The NSA cannot know in advance which tiny fraction of 1 percent of the records it may need, so it collects and keeps as many as it can - 27 terabytes, by one account, or more than double the text content of the Library of Congress' print collection.
The location programs have brought in such volumes of information, according to a May 2012 internal NSA briefing, that they are "outpacing our ability to ingest, process and store" data. In the ensuing year and a half, the NSA has been transitioning to a processing system that provided it with greater capacity.
The possibility that the intelligence community has been collecting location data, particularly of Americans, has long concerned privacy advocates and some lawmakers.
Three Democratic senators - Ron Wyden of Oregon, Mark Udall of Colorado, and Barbara A. Mikulski of Maryland - have introduced an amendment to the 2014 defense spending bill that would require U.S. intelligence agencies to say whether they have ever collected or made plans to collect location data for "a large number of United States persons with no known connection to suspicious activity."
NSA director Keith Alexander disclosed in Senate testimony in October that the NSA had run a pilot project in 2010 and 2011 to collect "samples" of U.S. cellphone location data. The data collected were never available for intelligence analysis purposes, and the project was discontinued because it had no "operational value," he said.
Alexander allowed that a broader collection of such data "may be something that is a future requirement for the country, but it is not right now."
The number of Americans whose locations are tracked as part of the NSA's collection of data overseas is impossible to determine from the Snowden documents alone, and senior intelligence officials declined to offer an estimate.
"It's awkward for us to try to provide any specific numbers," one intelligence official said in a telephone interview.
An intelligence lawyer, speaking with his agency's permission, said location data are obtained by methods "tuned to be looking outside the United States," a formulation he repeated three times. When U.S. cellphone data are collected, he said, the data are not covered by the Fourth Amendment, which protects Americans against unreasonable searches and seizures.