The FBI has stepped in to help investigate a cybersecurity event at Louisville, Ky.-based Norton Healthcare, CBS affiliate WLKY reported May 17.
The event, which started May 9 and the health system is not calling an attack, forced the hospital to temporarily shut down its email and internet access.
Norton said it received a fax from hackers that contained "threats and demands," according to the report.
The hospital did not disclose what threats and demands were made against it in the fax, nor did it include if the alleged hackers demanded ransom.
The cause of the event is unknown.
"Despite all the precautions we have taken and significant resources we dedicate to cyber security, we were still the victim of a crime here," Renee Murphy, senior vice president and chief marketing and communications officer of Norton Healthcare, told the publication.
Norton said its investigation into the incident is ongoing.