HACKENSACK - Thousands of patients at three northern New Jersey hospitals have been alerted that their personal information was stolen by a billing clerk in a data breach.

The Record newspaper reports the billing company said in a letter to patients that it's cooperating with federal authorities in their "criminal investigation."

Officials say an employee with Medical Management LLC, which handles billing at The Valley Hospital in Ridgewood, Englewood Hospital and Medical Center and Holy Name Medical Center in Teaneck passed on names, Social Security numbers and birth dates of patients.

The North Carolina-based billing company contracts with 40 providers across the country.

The employee worked at the company from February 2013 until March 2015 when the breach was discovered.