In March 2015, Primera Blue Cross in Washington State (premera.com) was victim of a cyberattack where 11 million customers were affected. Hackers were able to penetrate the system on May 5, 2014 but it was not discovered until January 29, 2015. Sensitive data like SSN, DOB, email address and other account information was compromised.
Here are a couple of links with some information about the incident.
http://krebsonsecurity.com/2015/03/premera-blue-cross-breach-exposes-financial-medical-records/
https://www.premera.com/wa/visitor/about-the-cyberattack/?WT.z_redirect=www.premera.com/cyberattack/
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