INDIANAPOLIS — Health insurer Anthem said hackers infiltrated its computer network and gained access to a host of personal information for customers and employees, including CEO Joseph Swedish.

The breach impacted customers and employees of Anthem Blue Cross and Blue Shield in Maine, the company said, although it did not specify how many. Anthem has about 312,000 customers and more than 800 employees in the state.

“Anthem Blue Cross and Blue Shield in Maine will individually notify current and former members whose information has been accessed,” company spokesman Rory Sheehan said in a written statement. ” Credit monitoring and identity protection services will be provided free of charge so that those who have been affected can have peace of mind.”

The nation’s second-largest health insurer said it was contacting customers affected by the “very sophisticated” cyberattack and was working to figure out how many people were affected.

The company said information the hackers gained access to included names, birthdates, email address, employment details, Social Security numbers, incomes and street addresses of people who are currently covered or have had coverage in the past.

The Indianapolis-based insurer said credit card information wasn’t compromised, and it has yet to find evidence that medical information such as insurance claims and test results was targeted or obtained.

Anthem Inc., which recently changed its name from WellPoint, runs Blue Cross Blue Shield plans in more than a dozen states, including California, New York and Ohio. It covers more than 37 million people.

The insurer said all of its product lines were affected. It sells mainly private individual and group health insurance, plans on the health care overhaul’s public insurance exchanges and Medicare and Medicaid coverage. It also offers life insurance and dental and vision coverage.

Affected brands include Anthem Blue Cross, Blue Cross and Blue Shield of Georgia, Empire Blue Cross and Blue Shield and Amerigroup.

Anthem said Wednesday evening that the FBI is investigating and the company has hired Internet security company Mandiant to improve its network defenses. The insurer will provide free credit monitoring and identity protection services.

The FBI urged Anthem customers contacted by the insurer to report suspected instances of identity theft.

In 2013, the insurer agreed to pay $1.7 million to resolve allegations it left the information of more than 612,000 members available online because of inadequate safeguards. The U.S. Department of Health and Human Services said that security weaknesses in an online application database left names, birthdates, addresses, telephone numbers, Social Security numbers, and health data accessible to unauthorized users.

The Health and Human Services Department said then that the insurer didn’t have adequate policies for authorizing access to the database, didn’t perform a needed technical evaluation after a software upgrade, and did not have technical safeguards to verify that the people or entities seeking access were authorized to view the information in the database.

Staff writer J. Craig Anderson contributed to this story.