New York (CNN Business) A day after Quest Diagnostics said its customers' data has potentially been compromised, rival LabCorp said its patients' personal information may have been exposed, too.

LabCorp said its third-party billing collections vendor, American Medical Collection Agency, notified the bloodwork company that hackers gained access to AMCA's online payment system. The unauthorized access took place between August 1, 2018, and March 30, 2019, LabCorp said.

The company said it has referred millions of customers to AMCA for billing collections, and 7.7 million customers had their data stored in the hacked system.

AMCA's system stored customers' first and last names, credit card and bank account numbers, birth dates, addresses, phone numbers, dates of service, health care provider information, and the amount customers owed. LabCorp said it did not provide AMCA with information about tests, lab results, or diagnostic information. AMCA said it did not store Social Security numbers.

LabCorp LH said it believes about 200,000 customers' credit card or bank account information may have been accessed, and it is sending notices to those customers. It said AMCA plans to offer affected customers identity protection and credit-monitoring services for two years.

Read More