Community Health Systems, which operates 11 hospitals in Alabama, announced Monday that it had a data breach that affected an estimated 4.5 million patients.

Greenville’s L.V. Stabler Memorial Hospital and Stabler Clinic are operated by CHS.

In a statement filed with the Securities and Exchange Commission, CHS reported a hacker in China bypassed the company’s security measures. The attack likely took place in April and June of this year.

L.V. Stabler Memorial Hospital spokesman David Norrell said that the hospital was not affected by the breach, but that Stabler Clinic was.

In a statement, L.V. Stabler Memorial Hospital officials said: “Limited personal identification data belonging to some patients who were seen at Stabler Clinic over the past five years was transferred out of our organization in a criminal cyber attack by a foreign-based intruder. The transferred information did not include any medical information or credit card information, but it did include names, addresses, birthdates, telephone numbers and social security numbers.

We take very seriously the security and confidentiality of private patient information and we sincerely regret any concern or inconvenience this event may cause for our patients. Though we have no reason to believe that this data would ever be used, all affected patients are being notified by letter and offered free identity theft protection.”

Besides L.V. Stabler Memorial Hospital, CHS operates Trinity Medical Center in Birmingham, Crestwood Medical Center in Huntsville, Gadsden Regional Medical Center; Home Care in Attalla; Flower’s Hospital in Dothan; Cherokee Home Health in Centre; Stringfellow Memorial Hospital in Anniston; South Baldwin Regional Medical Center in Foley; DeKalb Regional Medical Center in Fort Payne; and Riverview Regional Medical Center in Gadsden.