Cybercriminals attacked the computer systems of a California-based health care provider causing emergency rooms in multiple states to close and ambulance services to be redirected.

The ransomware attack happened at Prospect Medical Holdings of Los Angeles, which has hospitals and clinics in Connecticut, Pennsylvania, Rhode Island and Texas. Prospect Medical is working on resolving the issue, the company said in a statement Friday.

“Prospect Medical Holdings, Inc. recently experienced a data security incident that has disrupted our operations,” the company said in a statement. “Upon learning of this, we took our systems offline to protect them and launched an investigation with the help of third-party cybersecurity specialists. While our investigation continues, we are focused on addressing the pressing needs of our patients as we work diligently to return to normal operations as quickly as possible.”

Officials with the Pennsylvania Association of Staff Nurses and Allied Professionals, the nurses union at Springfield-based Crozer-Chester Medical System, say the hospital has reverted to a paper system because most of the computers are offline, CBS News reported. The computers are unlikely to be back online until next week, according to the labor group. 

Elective surgeries, urgent care centers closed

The data breach forced the emergency departments Manchester Memorial and Rockville General in Connecticut to close Thursday. Hospital officials there diverted patients to nearby medical centers. All Prospect Medical-owned health care facilities “are experiencing IT complications” and many services including elective surgeries and urgent care has been closed, the company posted on its website. 

“Our computer systems are down with the outage affecting all Waterbury Health inpatient and outpatient operations,” Prospect Medical’s hospital in Waterbury, Connecticut, posted on its Facebook page. “We are in the process of reevaluating our downtime capabilities and may reschedule some appointments. Affected patients will be contacted.”

In Pennsylvania, the attack affected services at facilities including: the Crozer-Chester Medical Center in Upland, Taylor Hospital in Ridley Park, Delaware County Memorial Hospital in Drexel Hill and Springfield Hospital in Springfield, the Philadelphia Inquirer reported.

—The Associated Press contributed to this report