SAN FRANCISCO (CBS SF) — The second largest health insurer in the nation is dealing with a massive data breach Wednesday night.

Anthem says hackers broke into a database containing personal information for tens of millions of members, an attack the insurer described as “very sophisticated.”

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“Anthem’s own associates’ personal information – including my own – was accessed during this security breach. We join you in your concern and frustration, and I assure you that we are working around the clock to do everything we can to further secure your data,” Anthem President Joseph Swedish said in a statement posted on their website.

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Anthem offers Blue Cross Blue Shield plans in California.

The company says names, addresses, birth dates, and social security numbers may have been exposed, but medical and financial information appeared to be safe.

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Anthem said they were in the process of notifying members and said they would provide credit monitoring and identity theft services free of charge to affected customers.