The FBI and Department of Homeland Security periodically release such alerts to provide U.S. businesses with technical information they can use to either prevent or identify cyber attacks.
The FBI's alert to health care companies did not identify any specific victims targeted by hackers. An agency spokesman declined comment when asked about the document.
Community Health Systems, the No. 2 U.S. publicly traded hospital operator, disclosed the attack on Monday, saying stolen data included patient names, addresses, birth dates and Social Security numbers.
—By Reuters