WASHINGTON — Mathematician William Binney worked for the National Security Agency for four decades, and in the late 1990s he helped design a system to sort through the digital data the agency was sucking up in the exploding universe of bits and bytes.
When the agency picked a rival technology, he became disillusioned. He retired a month after the terrorist attacks of Sept 11, 2001, and later went public with his concerns.
Binney and several other former NSA employees said that the cyber-spying agency had created a massive digital dragnet to secretly track communications of Americans. Government officials denied the allegations and dismissed Binney and the others as conspiracy theorists who lost a bureaucratic fight.
Revelations from Edward Snowden, the former NSA contractor who leaked secrets to the media, have made it clear that the NSA has been collecting and storing millions of domestic phone records every day — numbers, time and location, but not content — for at least seven years.
Another program, known as PRISM, has given the NSA access since at least 2007 to emails, video chats and other communications through U.S. Internet companies to spy on foreigners. American emails inevitably were swept up as well.
Were Binney and his colleagues right? Is the NSA conducing secret surveillance of Americans?
U.S. intelligence officials and senior members of Congress say no. They say authorities need a court order to actually use data gathered by the NSA on "U.S. persons," and only for investigations into terrorism or foreign espionage. If your data is sitting on an NSA server somewhere but is never examined, they argue, is your privacy really being invaded?
"What we create is a set of data … and only under specific times can we query that data," Gen. Keith Alexander, the NSA director, told a Senate committee Wednesday. "And when we do that it's auditable…. We don't get to swim through the data."
James R. Clapper, director of national intelligence, used the metaphor of a library catalog system. All the telephone metadata goes into the library, but taking a specific book "off the shelf, opening it up and reading it" would require a warrant, he told NBC News.
And Sen. Dianne Feinstein (D-Calif.), who chairs the Senate Intelligence Committee, said the "vast majority" of records are never accessed and are deleted after five years.
Civil liberties activists aren't convinced.
Phone records are "sensitive as hell," said Julian Sanchez, who blogs on privacy at the Cato Institute, a libertarian think tank. "Who called a suicide hotline? Who called a divorce lawyer? A substance abuse counselor? Their gynecologist, followed by Planned Parenthood?"
NSA officials say that kind of information is irrelevant to the agency. It is tasked with collecting foreign intelligence and stopping terrorist plots, they say, and analysts would not be authorized to examine records on Americans unless they showed a link to a terrorism suspect or a foreign agent. All of the surveillance programs Snowden revealed, they add, were approved by Congress and are supervised by federal judges.
Critics say assurances about limits, rules and oversight would be more convincing if not for Snowden himself: He was able to remove highly classified documents from an NSA facility in Hawaii that officials say he was not authorized to access.
"Here's a low-level systems guy" who copied a top-secret order from the Foreign Intelligence Surveillance Court and a presidential directive about cyber attacks, said Mark Rumold, an attorney with the Electronic Frontier Foundation, a nonprofit advocacy group in San Francisco. "To say that there is a rigorous technical program in place to prevent broad-based lurking around through the data — I have a hard time believing that."
In a lawsuit, Rumold's group argues the NSA has used a "shadow network of surveillance devices" to acquire communications "of practically every American who uses the phone system or the Internet … in an unprecedented suspicionless general search through the nation's communications networks."
The group cites evidence from Mark Klein, who in 2006 went public with documents purporting to show a secret room at an AT&T; facility in San Francisco where he believed the NSA was copying telecommunications traffic. AT&T; lawyers have acknowledged in court that the documents are genuine — without confirming that they show what Klein believes.
Klein said what he found was consistent with Snowden's disclosures on NSA programs code-named Fairview and Blarney, which involved the collection of communications on fiber cables and infrastructure as data flows past, as well as the PRISM program that accesses data from Internet companies.
Although the programs target foreigners, data on Americans are also captured. It is supposed to be discarded or blacked out under a process called minimization.
Officials decline to say precisely how minimization works, or whether the NSA collects more information on Americans than it has acknowledged.
The information black hole puzzles Fred Cate, a law professor at Indiana University who advises the Pentagon on privacy issues.
It is "complete and utter nonsense," Cate says, to argue that answering questions about NSA surveillance would help America's enemies.
Foreign governments and terrorists already know the NSA is targeting their telephones, emails and other communications, Cate said. "That's why Osama bin Laden's compound wasn't connected to the Internet," he added.