There’s been a security breach of patient information at a Detroit hospital.

Officials at Detroit Medical Center’s Harper Hospital say an employee who worked at the facility was found with personal information of more than 1,000 patients, including name, birthdate and, in some cases, social security number.

West Bloomfield Police came across the documents during an identity theft investigation.

DMC officials said that when they were notified, they initiated an internal review and immediately revoked the employee’s access to its computer systems and all of the DMC hospitals.

Letters have been sent to all affected by this breach and the patients have been offered free credit monitoring.