Insurance giant Aflac identified “suspicious activity” in its U.S. network, which initiated its cybersecurity protocols. Aflac said it was able to stop the attack within hours, and its systems were not affected by ransomware.

The insurer said it’s in the early stages of a review of the incident, and so far is unable to determine the total number of affected individuals.

The company confirmed today that it was breached by hackers, who may have stolen sensitive information from its millions of customers. Here’s what to know. Aflac Incorporated (NYSE: AFL) was the most recent target of a “sophisticated cybercrime group” that has led a campaign against a number of insurance companies in recent weeks,