Feb 4 - Health insurer Anthem Inc, which has nearly 40 million US customers, said late on Wednesday that hackers had breached one of its IT systems and stolen personal information relating to current and former consumers and employees.

The No. 2 health insurer in the United States said the breach did not appear to involve medical information or financial details such as credit card or bank account numbers.

The information accessed during the "very sophisticated attack" did include names, birthdays, social security numbers, street addresses, email addresses and employment information, including income data, the company said.

Anthem said that it immediately made every effort to close the security vulnerability and reported the attack to the FBI. Cybersecurity firm FireEye Inc said it had been hired to help Anthem investigate the attack.

The company did not say how many customers and staff were affected, but the Wall Street Journal earlier reported it was suspected that records of tens of millions of people had been taken, which would likely make it the largest data breach involving a US health insurer.