US hospitals have been severely affected by a substantial cyberattack, leading to the closure of emergency rooms in multiple states and the redirection of ambulances. The attack started on Thursday and targeted computer systems managed by Prospect Medical Holdings, a California-based healthcare company that operates clinics and hospitals in Texas, Connecticut, Rhode Island, Pennsylvania, and its home state.

As a precaution, Prospect Medical took its systems offline after detecting the data security incident and sought assistance from cybersecurity experts to assess the scale of the attack and formulate a solution. While the investigation is ongoing, the company emphasizes its focus on catering to the immediate needs of its patients and restoring operations as swiftly as possible.

The recent cyberattack has disrupted medical facilities across states. In Connecticut, emergency departments at Manchester Memorial and Rockville General hospitals closed for a significant duration on Thursday, with patients redirected to nearby centers. Though the emergency departments resumed operations late Thursday, many primary care services stayed closed on Friday.

Reports of similar disruptions have emerged from other facilities across the system. In Pennsylvania, services at multiple facilities, including Crozer-Chester Medical Center and Taylor Hospital, were affected. In California, Prospect Medical’s seven hospitals have also been impacted, though no immediate response was received from the hospitals’ representatives.