Clinical laboratory services company Quest Diagnostics announced Monday that it is investigating a third-party hack into an internet application on its network.

The Madison, New Jersey-based Fortune 500 healthcare company said in a press release that on Nov. 26, an unauthorized third party accessed the MyQuest by Care 360 internet application and obtained health information of about 34,000 patients.

In its statement, the company said the data accessed by the third party "included names, dates of birth, lab results and, in some instances, phone numbers."

None of the compromised information included Social Security numbers, credit card, insurance or other financial information, Quest says. The company says it immediately addressed the hack when it was discovered and has notified all affected individuals.

There is an investigation underway, and the company says it is working with a cybersecurity firm to determine the source and cause of the breach.

Anyone with questions on the incident can call Quest Diagnostics at (888) 320-9970 Monday through Friday between 9 a.m. and 7 p.m. Eastern Time.