The National Security Agency said Thursday it collected more domestic call records than allowed, and as a result has been mass-deleting call records from across a three-year period.

The NSA said in a statement that on May 23 it "began deleting all call detail records (CDRs) acquired since 2015 under Title V of the Foreign Intelligence Surveillance Act."

Weeks before the deletions began, the Office of the Director of National Intelligence reported that the NSA acquired more than 534 million domestic call records in 2017, triple the amount collected in 2016.

The NSA's power to collect these records was curtailed by the 2015 USA Freedom Act, which ended the once-secret dragnet collection of domestic call records and replaced it with a system in which companies supplied records of targets and their contacts as needed.

"NSA is deleting the CDRs because several months ago NSA analysts noted technical irregularities in some data received from telecommunications service providers," the agency said in its statement.

The irregularities "resulted in the production to NSA of some CDRs that NSA was not authorized to receive," the statement said.

The NSA said it notified congressional oversight committees and the Privacy and Civil Liberties Oversight Board. The agency said it also informed the Justice Department, which notified the Foreign Intelligence Surveillance Court.

"Because it was infeasible to identify and isolate properly produced data, NSA concluded that it should not use any of the CDRs. Consequently, NSA, in consultation with the Department of Justice and the Office of the Director of National Intelligence, decided that the appropriate course of action was to delete all CDRs," the NSA said.

The NSA's privacy practices are subject to several lawsuits, though many cases against the agency's call record dragnet were dismissed as moot after passage of the Freedom Act.

It's not immediately clear if any group will argue the deletion violates active preservation of evidence orders. Attorneys at the Electronic Frontier Foundation, one prominent group with preservation orders, did not immediately respond to a request for comment.

The EFF has court orders preventing the NSA from deleting vast swaths of data, including five years worth of dragnet call record data spanning 2010 to 2015. That data must be stored in non-searchable form, pursuant to surveillance court orders. EFF views data preservation as necessary to prove alleged violations of the Fourth Amendment.

In October, the NSA admitted that it deleted some records it had been ordered to preserve. The records included internet communications intercepted from 2001 to 2007.

Conservative legal activist Larry Klayman, whose lawsuits against the call record program were dismissed as moot, said he views the deletions as an illegal cover-up.

"This is an effort to take all that evidence off the market and to protect the intelligence community, the deep state. I wasn't given notice and we have cases pending on appeal," Klayman told the Washington Examiner.

After winning a major ruling in December 2013 that the NSA's call record collection likely violated the Fourth Amendment, Klayman argued unsuccessfully that his lawsuits weren't undercut by the Freedom Act.

"Obviously, they're destroying evidence," Klayman said. "It's calculated to take evidence off the market and it's obstruction of justice. The intelligence agencies continued to violate the new law. They have no respect for the law. They think they're above the law."

The Freedom Act was supposed to dramatically limit domestic call record collection — a practice exposed in June 2013 by former NSA contractor Edward Snowden. But the reforms divided privacy advocates. Many original House co-sponsors of the legislation voted against the final bill, arguing it didn't go far enough, as did Sen. Rand Paul, R-Ky.

Going forward, the NSA said in its statement that it will only collect call records that it's authorized to take.

"The root cause of the problem has since been addressed for future CDR acquisitions, and NSA has reviewed and revalidated its intelligence reporting to ensure that the reports were based on properly received CDRs," the agency said.

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