A group of cybercriminals hacked into data systems at insurance company Aflac, possibly gaining access to sensitive information such as Social Security numbers and health reports, the company said on Friday.

It’s the largest insurance company yet to fall victim to a major hacking, with tens of millions of customers and a $55 billion market cap.

American insurance giant Aflac disclosed that its systems were breached in a broader campaign targeting insurance companies across the United States by attackers who may have stolen personal and health information.