Updated

Sensitive information on about 1,000 patients at Walter Reed Army Medical Center and other military hospitals was exposed in a security breach, sparking identity theft concerns and an investigation by the Army.

Names, Social Security numbers, birth dates and other information was accessed, hospital officials said Monday. The computer file that was breached did not include information such as medical records, or the diagnosis or prognosis for patients, they said.

Walter Reed officials declined to explain exactly how the information was compromised, pending an ongoing investigation by the hospital and the Army. They would only say that the computer file was found on a "non-government, non-secure computer network."

The medical center learned of the breach on May 21 from an outside data mining company, which officials did not identify. They said the company was working for another client, found the file and contacted Walter Reed.

The hospital said it is working to notify all of the people named in the data file. Letters or e-mails were being sent out, beginning Monday.

Walter Reed plans to offer free credit protective services to patients whose information was revealed.

The hospital also has set up a hotline for people to call to see if their information was disclosed (1-877-854-8542, ext. 9).