Anthem, the second-largest health insurer in the United States, said it was hacked late Wednesday, and that hackers stole as many as 80 million personal records.

The company, formerly known as WellPoint, described the incident as a “very sophisticated external cyber attack,” according to a statement from CEO Joseph Swedish.

Here’s an overview of what you should know about the attack, and how you might be affected:

How do I know if I was affected?

Anthem’s website says it will notify via mail everyone whose information was stolen. The letters are expected to be mailed “in the coming weeks.”

Although the company hasn’t yet determined all the customers who were impacted, it’s possible that anyone with an insurance plan under Anthem Blue Cross, Anthem Blue Cross and Blue Shield, Amerigroup, Blue Cross and Blue Shield of Georgia, Caremore, DeCare, Empire Blue Cross and Blue Shield, Healthlink and Unicare could have been affected.

How can I protect myself?

According to Swedish’s statement, Anthem “will provide credit monitoring and identity protection services free of charge so that those who have been affected can have peace of mind.” In the aforementioned letters, the company will inform customers how they can protect themselves, and what it is offering by way of protection, according to Anthem’s website.

The FBI, which is investigating the hack, has asked Anthem customers to report any incidents of suspected identity theft in the coming weeks.

What information might have been stolen?

The hackers accessed customer names, email addresses, Social Security numbers, income and other employment information, street addresses and birthdates. But there is “no evidence that credit card or medical information, such as claims, test results or diagnostic codes were targeted or compromised,” Swedish said.

What is Anthem doing to address the problem?

In addition to notifying affected customers via mail and pledging to give them free credit monitoring and identity protection services, Swedish said it immediately reached out to the FBI, and hired cybersecurity firm Mandiant to analyze holes in the company’s digital security.

In 2013, Anthem agreed to dole out $1.7 million after it allegedly left the data of around 612,000 customers exposed to potential hackers. That data included names, addresses, phone numbers, birthdates, Social Security numbers and health information.

The company also offered free credit monitoring to around 128,000 customers in 2008, after some of their personal information was found to be accessible to unauthorized viewers online.

Have something to add to this story? Share it in the comments.