In a statement Monday, the company said there was an unauthorized third-party intrusion into an internet application on its network on November 26.
The hacked data included names, date of births, lab results, and in some instances, telephone numbers. The information did not include Social Security numbers, credit card information, insurance or other financial information.
The company says there is no indication that individuals' information has been misused in any way.
Quest Diagnostics has notified affected individuals via mail. They have also set up a dedicated toll-free number to call with questions regarding this incident. The number is (888) 320-9970, and can be reached Monday through Friday between 9 a.m. and 7 p.m.
Quest says it is taking steps to prevent similar incidents from happening in the future, and is working with a leading cybersecurity firm.
They have reported the hack to law enforcement and the investigation continues.