Quest Diagnostics issued a statement that billing collections service American Medical Collection Agency (AMCA) had potential unauthorized activity on AMCA’s web payment page, which could have compromised the data of about 11.9 million Quest patients.  Lab results were not affected by this incident.  Quest Diagnostics is continuing their investigation.

Update: LabCorp also revealed in an SEC filing that AMCA also had 7.7 million of their customer records affected in a similar incident.