Quest Diagnostics says millions of its patients may have had their personal and medical information exposed in a data breach.
Quest said in a statement Monday that a billing collection services provider it works with experienced the breach on its web payment system.
The provider said an unauthorized user had access to its system, which contained information on approximately 11.9 million Quest patients. That information includes certain financial data, Social Security numbers and medical information, but not lab test results.
Quest, which is one of the biggest medical testing companies in the U.S., says it's still looking into the matter and is working with "forensic experts."