WASHINGTON — The National Security Agency admitted in documents released Tuesday that it had wrongly put 16,000 phone numbers on an "alert list" so their incoming calls could be monitored, a mistake that a judge on the secret surveillance court called a "flagrant violation" of the law.
The documents are the latest to show that not only did the secret spy agency collect more data than most Americans suspected, its agents sometimes went too far when tapping into the data.
In 2006, the NSA asked for and won approval from the Foreign Intelligence Surveillance Court, or FISC, to routinely collect the dialing records of domestic phone calls. The judges, to the surprise of some outside lawyers, agreed that all of these phone records could be "relevant" to an investigation, and therefore, could be collected.
The agency insisted, however, that it would hold these records and tap into them only when it had a "reasonable and articulable suspicion" that a phone number was linked to a suspected terrorist.
But in January 2009, top officials of the intelligence agency learned that about 18,000 phone numbers were on the "alert list" that could subject them to daily monitoring. Of these, about 16,000 had not been shown to be reasonably linked to a terrorist. The agency notified the judges of the mistake and said they were making needed changes in their software that tracked phone numbers.
Judge Reggie Walton, a member of the special court, said he was "very disturbed" about the incident and said the agency's explanation "strains credulity."
"The court is exceptionally concerned about what appears to be a flagrant violation of its order in this matter," Walton wrote.
On Tuesday, NSA officials said the documents showed the agency had admitted its mistakes and taken steps to correct them and comply with the law. They also emphasized that there is no evidence that the agency improperly spied on Americans and used secret information for political or other improper purposes.
James R. Clapper, director of national intelligence, blamed the mistakes on the "complexity of the technology" used to gather all the phone data.
"These gaps in understanding led, in turn, to unintentional misrepresentations in the way the collection was described to the FISC," Clapper said. "There was no single cause of the incidents, and in fact, a number of successful oversight, management and technology processes in place operated as designed and uncovered these matters."
The Electronic Frontier Foundation and the American Civil Liberties Union sued and sought the documents under the Freedom of Information Act. They "showed that the NSA repeatedly violated court-imposed limits on its surveillance powers, and they confirm that the agency simply cannot be trusted with such sweeping authority," ACLU attorney Alex Abdo said.
Last month, leaked documents revealed that the NSA had overstepped its authority to seize emails. But most of the abuses were said to be technical errors.