LONDON — Britain's health service was hit Friday by a huge international cyberattack that froze computers at hospitals across the country — an attack that shut down wards, closed emergency rooms and brought medical treatments to a screeching halt.
Hospitals in areas across Britain found themselves without access to their computers or phone systems. Many canceled all routine procedures and asked patients not to come to the hospitals unless it was an emergency. Some chemotherapy patients were even sent home because their records could not be accessed.
Most of the affected hospitals were in England, but several facilities in Scotland also reported being hit. Doctors' practices and pharmacies reported similar problems.
As similar widespread ransomware attacks were reported in Spain, Romania and elsewhere, experts warned that online extortion attempts by hackers are a growing menace. Hospitals, with their often outdated IT systems and trove of confidential patient data, are a particularly tempting target.
British Prime Minister Theresa May said there was no evidence that patient data had been compromised in the attack, and that it had not specifically targeted the National Health Service.
"It's an international attack and a number of countries and organizations have been affected," she said.
NHS Digital, which oversees U.K. hospital cybersecurity, says the attack used the Wanna Decryptor variant of malware, which infects and locks computers while the attackers demand a ransom.
Pictures posted on social media showed screens of NHS computers with images demanding payment of $300 worth of the online currency Bitcoin, saying: "Ooops, your files have been encrypted!"