PITTSBURGH, Pa.(KDKA)- Quest Diagnostics is warning nearly 12 million customers about a possible data breach involving their personal information.

According to a statement released Monday, Quest’s billing collections service provider, American Medical Collection Agency (AMCA), notified them that an unauthorized user had access to AMCA’s system containing personal information AMCA received from various companies, including Quest. AMCA provides billing collections services to Optum360, which in turn is a Quest contractor.

AMCA believes the personal information includes financial data, Social Security numbers, and medical information. No laboratory test results were involved.

Quest and Optum360 were first notified on May 14, 2019 of potential unauthorized activity on AMCA’s web payment page. On May 31, 2019, AMCA notified Quest and Optum360 that the data on AMCA’s affected system included information regarding approximately 11.9 million Quest patients.

Quest has not been able to verify the accuracy of the information received from AMCA, however forensic experts are investigating the matter.

Since learning of the AMCA data security incident, Quest Diagnostics has suspended sending collection requests to AMCA.

Quest will be working with Optum360 to ensure that Quest patients are appropriately notified of the possible breach. Quest has dozens of locations in and around the Pittsburgh area.