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The National Security Agency collects less than 30 percent of U.S. phone records due to “technical challenges” involved with the influx of cellphone data, according to media reports.

The agency’s phone data collection has dropped significantly since 2006 as it struggles to keep pace with consumers’ shift away from landlines.

It has faced issues in customizing its system to handle the increase of cell data while not sweeping in cell tower and location-based information, which the agency is not legally authorized to obtain. The records include numbers called and call duration.

Eight years ago, the NSA was collecting “almost 100” percent of bulk call data, an anonymous senior U.S. official told the Washington Post Saturday.