Update: The hacking tool was leaked by the Shadow Brokers, which has been dumping stolen N.S.A. hacking tools online starting last year. Attacks are being reported in Britain and 11 other countries, including Turkey, Vietnam, the Philippines, and Japan - the majority of affected computers are in Russia.
Patient data throughout the NHS in Britain has been scrambled by ransomware known as WannaCryptor or WCry. The ransom demanded currently is $300 in bitcoin - presumably for each computer affected.
The BBC is reporting up to 25 NHS organizations and some GP practices have been affected.
There are reports of cyber-attacks affecting health organizations worldwide.
Prime Minister Theresa May has been informed of the situation and Health Secretary Jeremy Hunt is being briefed by the National Cyber Security Centre.
The NHS released the following statement: "NHS Digital is working closely with the National Cyber Security Centre, the Department of Health and NHS England to support affected organisations and ensure patient safety is protected.
"Our focus is on supporting organisations to manage the incident swiftly and decisively, but we will continue to communicate with NHS colleagues and will share more information as it becomes available."
The BBC is reporting: A GP from a surgery in York said: "We received a call from York CCG [Clinical Commissioning Group] around an hour ago telling us to switch off all of our computers immediately."
Dozens of hostpitals are effectively shut-down, only accepting patients with loss of consciousness or heavy blood loss.
Fire alarms at Newark Hospital, in Nottinghamshire are going off so local fire services are being affected as well as hospital staff.