WannaCry cyber attack hits the NHS

A global cyber attack has hit hospitals and GP surgeries across England and Scotland, forcing some to cancel operations and divert ambulances.

The attack began on 12 May and spread to computers in around 150 countries. It used ransomware called WannaCry, which locks files and demands a payment in the digital currency Bitcoin to release them.

NHS disruption

Dozens of NHS organisations were affected. Staff were forced to switch to pen and paper, and some hospitals asked patients not to attend unless it was an emergency. Appointments and operations were cancelled, and some ambulances were sent to other hospitals.

Screens displayed a message demanding $300 worth of Bitcoin to unlock each computer, with the ransom rising if it was not paid within three days.

The Prime Minister, Theresa May, said there was no evidence that patient data had been compromised, and that the attack was not specifically aimed at the NHS.

A worldwide attack

The attack affected businesses and organisations around the world, including the Spanish telecoms company Telefonica, the German rail operator Deutsche Bahn, the delivery company FedEx and factories run by the carmakers Renault and Nissan, including its plant in Sunderland.

The ransomware spread by exploiting a weakness in older versions of Microsoft Windows. The flaw was reportedly discovered by the American National Security Agency, and details of it were leaked online earlier this year.

Microsoft released a fix in March, but many computers had not been updated. Some NHS computers were still running Windows XP, which Microsoft stopped supporting in 2014.

An accidental hero

The spread of the attack was slowed when a young British security researcher found a "kill switch" in the software. By registering a web address that the program was checking, he stopped it from spreading further.

Questions for the government

The attack has raised questions about how well the NHS protects its computer systems and whether enough money has been spent on updating old equipment. Opposition parties have accused the government of failing to act on warnings.

The National Cyber Security Centre, part of GCHQ, is working with the NHS to restore systems.

Experts are urging organisations and home users to install security updates and to back up their files.