Several U.S. states are investigating a massive cyberattack on No. 2 U.S. health insurer Anthem Inc. that a person familiar with the matter said is being examined for possible ties to China.

Anthem disclosed the attack late Wednesday, saying unknown hackers had penetrated a database with some 80 million records. The insurer said it suspected they had stolen information belonging to tens of millions of current and former customers as well as employees.

Attorneys general of Connecticut, Illinois, Massachusetts, Arkansas and North Carolina are looking into the breach, according to representatives of their offices and internal documents. California's Department of Insurance said it will review Anthem's response to the data attack.

A source familiar with the probe said a possible connection to China is being investigated, and the Wall Street Journal reported that people close to the investigation say some tools and techniques used against Anthem were similar to ones used in previous attacks linked to China.

The FBI said it is looking into the matter but did not discuss suspects.

Michael Daniel, President Barack Obama's cybersecurity adviser, speaking at a seminar in Washington, called the data breach "quite concerning" and warned consumers to change their passwords and monitor their credit scores.