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.

Aflac Inc. said a recent cybersecurity breach could have given intruders unauthorized access to customers’ personal information, including Social Security numbers, as well as health and claims data.