Anthem, one of the nation’s largest health insurers, said late Wednesday that the personal information of tens of millions of its customers and employees, including its chief executive, was the subject of a “very sophisticated external cyberattack.”

The company, which is continuing its investigation into the exact scope of the attack, said hackers were able to breach a database that contained as many as 80 million records of current and former customers, as well as employees. The information accessed included names, Social Security numbers, birthdays, addresses, email and employment information, including income data.

Anthem said no credit card information had been stolen, and it emphasized that it did not believe medical information like insurance claims or test results were compromised. It said hospital and doctor information was also not believed to have been taken.

Still, the attack, which was first reported by The Wall Street Journal, could be the largest breach of a health care company to date, and one of the largest ever of customer information.