The Latest: UK's health service hit by ransomware attack
NHS Digital, which oversees hospital cybersecurity, says the attack used the Wanna Decryptor variant of malware, which holds affected computers hostage 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!"
Bart's Health, which runs several London hospitals, said it had activated its major incident plan, cancelling routine appointments and diverting ambulances to neighboring hospitals.