The US National Security Agency (NSA) announced last week it was mass-deleting hundreds of millions of records of phone calls and text messages dating back to 2015.

The Agency said it was removing the data from its systems after NSA analysts spotted "technical irregularities in some data received from telecommunications service providers."

NSA admits it was receiving more metadata than allowed

The NSA is authorized under Title V of the Foreign Intelligence Surveillance Act (FISA) and through the USA Freedom Act of 2015 to collect call metadata on particular types of calls involving persons of interest that may pose a threat to national security.

But the NSA says it noticed this spring that it was receiving more call detail records (CDRs) that it was supposed to get under the current legal frame.

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.

NSA deleting three-years worth of call metadata

The NSA says malformed CDRs date back to 2015. The agency started the deletion process on May 23, this year, but only announced it last week.

"The root cause of the problem has since been addressed for future CDR acquisitions," the NSA said.

NSA officials said they reported the incident to supervising authorities, such as the Congressional Oversight Committees, the Privacy and Civil Liberties Oversight Board, and the Department of Justice (which, in turn, notified the Foreign Intelligence Surveillance Court).

In a blog post over the weekend, national security and civil liberties journalist Marcy Wheeler pointed out this was not the first time the NSA violated FISA law. She detailed five other incidents from the past years when the NSA admitted to improperly collecting and handling call metadata, although, this time the blame seems to be on the telcos who supplied the metadata.