The National Security Agency, since 2010, has been exploiting its huge data collection to create sophisticated graphs of some Americans' social connections.
The graphs can identity Americans' associates, their locations at certain times, their traveling companions and other personal information.
The revelation was made in newly disclosed documents and interviews with officials, the New York Times reports.
According to the report, the NSA began allowing the analysis of phone call and e-mail logs in November 2010 to examine Americans' networks of associations for foreign intelligence purposes after N.S.A. officials lifted restrictions on the practice.
The policy shift was intended to help the agency discover and track connections between intelligence targets overseas and people in the United States, according to an N.S.A. memorandum from January 2011.
The memorandum revealed that the agency was authorized to conduct 'large-scale graph analysis on very large sets of communications metadata without having to check foreignness' of every e-mail address, phone number or other identifier.
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N.S.A. officials have not revealed how many Americans have been caught up in the effort.
The documents do not describe what has resulted from the scrutiny, which links phone numbers and e-mails in a "contact chain" tied directly or indirectly to a person or organization overseas that is of foreign intelligence interest.
N.S.A. officials declined to identify which phone and e-mail databases are used to create the social network diagrams, and the documents provided by NSA whistleblower Edward Snowden do not specify them.
The documents show that significant amounts of information from the United States go into Mainway.