WASHINGTON, Jan 19 (Reuters) – The Federal Aviation Administration (FAA) said on Thursday a preliminary review found that contract personnel unintentionally deleted files prompting a nationwide groundstop on Jan. 11 that disrupted more than 11,000 flights.

The FAA said the issue occurred while personnel were working “to correct synchronization between the live primary database and a backup database” and the FAA added that it “has so far found no evidence of a cyber-attack or malicious intent.”

The FAA said it has made necessary repairs to the system “and has taken steps to make the pilot message system “more resilient.” (Reporting by David Shepardson; Editing by Sandra Maler)