SEATTLE — Premera Blue Cross said Tuesday approximately 11 million customers might be victims of a cyberattack on the health insurance company.

Premera, based in Mountlake Terrace, said it discovered the attack Jan. 29 but that it initially took place May 5, 2014.

The attack affects customers of Premera Blue Cross, Premera Blue Cross Blue Shield of Alaska, Vivacity and Connection Insurance Solutions. The company said the attackers might have gained access to customers’ information, including names, dates of birth, Social Security numbers, addresses, bank account information and claim information, according to a statement.