Aflac, one of the largest insurance companies in the United States, says hackers stole an unknown quantity of its customers’ personal information from its network during a cyberattack earlier this month.

Insurance company Aflac disclosed this week that cybercriminals breached its U.S. network and may have accessed customers’ personal information, the latest in a string of cyberattacks on insurance companies announced this month.

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.