Personal information for potentially tens of millions of HCA Healthcare patients has been stolen and is now available for sale on a data breach forum as of earlier this week.

HCA, one of the largest companies in the U.S., is the parent company of HCA Florida, and more than a hundred hospitals and clinics in Florida are impacted by this breach.

Here is what you need to know about the data hack:

What happened to the HCA Healthcare patient data?

HCA Healthcare released a statement Monday stating an unknown and unauthorized party got access to patients' names, addresses, emails, phone numbers, and birth dates, as well as the dates and locations of the patients' appointments.

HCA said they did not, however, get access to credit cards or account numbers, or social security numbers.

But DataBreaches.net reported Monday that the unnamed hacking group provided them with a sample set of data about a patient's "low risk" lung cancer assessment, which would apparently undercut HCA's assessment that no material or protected health information was breached.

Who is affected by this data breach?

The hack affects patients in nearly two dozen states, including patients at dozens of facilities in Florida and Texas.

The data sale was flagged on Twitter by Brett Callow, an analyst at New Zealand-based Emsisoft.

"This may be one of the biggest health care-related breaches of the year and one of the biggest of all time. That said, despite affecting millions of people, it may not be as harmful as other breaches as, based on HCA's statement, it doesn't seem to have impacted diagnoses or other medical information," Callow told CNBC.

Patient data breaches are not uncommon, but they can vary in scope and effect.

HCA's breach did not apparently include critical medical records, and the company said the breached data originated at an "external storage location exclusively used to automate the formatting of email messages."

What is HCA Healthcare doing about it?

HCA Healthcare will offer credit monitoring and identity protection services for patients who have been impacted.

But in the meantime, they're encouraging everyone to look out for spam calls, texts or emails.

Which South Florida HCA Healthcare locations were impacted?

HCA Florida Aventura Hospital, HCA Florida Kendall Hospital, HCA Florida Mercy Hospital, HCA Florida Miami International Cardiology were affected among many others.

For a full list of impacted Florida facilities click here.