The state of Montana is sending out notifications to 1.3 million people this week, warning them that a data breach on a state health department server last year may have revealed their personal information to hackers. That makes the population of potential victims greater than the entire population of Montana, which is about 1 million.

The attack occurred last July, according to state officials, but went undetected until May of this year. Information on the server included names, addresses, birth dates, Social Security numbers, medical records, and birth and death certificates.

The state is sending the letters to residents, former residents, and families of deceased residents who may have had their information compromised. State officials say they don't believe the hackers extracted any information, but encouraged potential victims to sign up for a credit monitoring service and insurance.