That third party - the American Medical Collection Agency (AMCA) - also recently notified competing firm Quest Diagnostics that an intrusion in its payments Web site exposed personal, financial and medical data on almost 12 million Quest patients.
Quest Diagnostics said that an unauthorized user had access to AMCA's personal information, including patients from Quest Diagnostics.
AMCA has not yet given detailed or complete information about the data breach to Quest or Optum360, the company said, including which information of which individuals may have been affected.
Quest said it's taking the matter "very seriously" and has suspended collections requests to AMCA.
Quest Diagnostics' laboratory test results were not given to AMCA and therefore weren't impacted by the breach, the company said.
Brad Keller, Program Director, Shared Assessments, pointed out that, in addition to Quest, it is reasonable to assume that AMCA has other customers whose customer information was accessed as well.
Quest will be working with Optum360 to ensure patients are appropriately notified. AMCA and Optum360 did not immediately respond to a request for comment from CNN Business. Headquartered in NY - the business capital of the world - FBN launched in October 2007 and is the leading business network on television, topping CNBC in Business Day viewers for the second consecutive year.
The data breach dates back to August 1 previous year through May 31. We hired a third-party external forensics firm to investigate any potential security breach in our systems, migrated our web payments portal services to a third-party vendor, and retained additional experts to advise on, and implement, steps to increase our systems' security.
"The Quest breach targeted mostly financial data, and personal information such as SSNs".
AMCA has been in contact with law enforcement regarding the incident, according to the SEC filing. Quest has dozens of locations in and around the Pittsburgh area.