Universal Health Services, which operates more than 250 hospitals across North America, started experiencing outages Sunday night that logged all staff out of computer systems and blocked them from logging back in, Bleeping Computer first reported.
Staff were instructed to conduct all business using pen and paper a protocol that was still in place as of Tuesday afternoon, according to one UHS employee based in Arizona.
When reached for comment, UHS spokesperson directed Business Insider to the company's online statements and added that none of UHS' overseas hospitals have been affected.
Ransomware attackers use malicious code to compromise an organization's computer systems and then demand that victims pay up in order to regain access.
The Arizona UHS employee told Business Insider that, as of Tuesday afternoon, employees haven't received any communication beyond the information posted to UHS' website. Because they have been locked out of their email accounts, employees are relying on a separate app called ShiftHound to coordinate shifts.
Attacks against hospitals have increased amid COVID-19, according to a report from Microsoft, as hospitals turn to new, unfamiliar telemedicine platforms and are increasingly cash-strapped during the pandemic.
Hackers see hospitals as valuable targets because their systems are crucial to patients' wellbeing, making them more likely to pay a ransom.