A billing service working with Quest Diagnostics — one of the largest medical lab services companies in the world, with dozens of locations in New Jersey — has suffered a data breach that could put nearly 12 million patients' information at risk.

Quest announced Monday morning American Medical Collection Agency — a billing collections service provider for Question contractor Optum360 — informed it on May 14 of "potential unauthorized activity on AMCA’s web payment page." Then on May 31, it told AMCA told the companies the data affected included information regarding about 11.9 million Quest patients.

"AMCA believes this information includes personal information, including certain financial data, Social Security numbers, and medical information, but not laboratory test results," Quest said in its statement.

But AMCA hasn't yet provided it with "detailed or complete" information about the securiy breach, including which information may have been affected, it said. Quest also hasn't been able to independently verify the information provided by AMCA so far, it said.

"Quest is taking this matter very seriously and is committed to the privacy and security of our patients’ personal information. Since learning of the AMCA data security incident, we have suspended sending collection requests to AMCA," Quest said.

It will be working with Optum360 to notify patients, it said.

Quest is headquartered in Secaucus, New Jersey.

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