A massive ransomware campaign has infected organisations in the UK, US, China, Russia, Spain, Italy, Vietnam, Taiwan and others, including UK's National Health Service.

Jakub Kroustek of Avast said on Twitter the security firm had detected "36,000 detections of #WannaCry (aka #WanaCypt0r aka #WCry) #ransomware so far. Russia, Ukraine, and Taiwan leading. This is huge." According to screenshots that have appear online from infected systems, the program locks computers and demands a payment in Bitcoin in order to unlock them.

Cyber extortionists tricked victims into opening malicious malware attachments to spam emails that appeared to contain invoices, job offers, security warnings and other legitimate files. The ransomware encrypted data on the computers, demanding payments of $300 to $600 to restore access. Security researchers said they observed some victims paying via the digital currency bitcoin.

Cyber-security firm Kaspersky said that the ransomware had been spotted cropping up in 100 countries and that the number was still growing. Kurt Baumgartner, principal security researcher at Kaspersky, said the malware has translations in dozens of languages, such that instructions for paying the ransom are displayed in the language set for that computer.

Malwarbytes also reported a ransomware on the block, part of the Necurs spam campaigns. The "Jaff" ransomware asks for an astounding 2 BTC, which is about $3,700, according to Malwarebytes.

Forcepoint Security Labs said that "a major malicious email campaign" consisting of nearly five million emails per hour was spreading the new ransomware. The group said in a statement that the attack had "global scope", affecting organisations in Australia, Belgium, France, Germany, Italy, Mexico, Taiwan and Russia.

F-Secure on Friday said it had gotten reports from more than 60 countries. Mikko Hypponen, its chief research officer, calls it "the biggest ransomware outbreak in history."

Researchers believe a criminal organization is behind this, given its sophistication.

Hospitals and doctors' surgeries across England were forced to turn away patients and cancel appointments on Friday after the 'ransomware' cyber attack crippled some computer systems in the state-run health service.

U.K.'s National Health Service (NHS) said 16 organizations had been affected by the cyber attack but said it had not been specifically targeted. No patient data was believed to have been accessed by the ransomware attack but it was unclear whether it had impacted any emergency cases.

Spain's government said on Friday a large number of companies, including telecommunications giant Telefonica, had been attacked by cyber criminals who infected computers with ransomware.

Portugal Telecom was also hit by a cyber attack but no services were impacted, a spokeswoman for the company said.

Power firm Iberdrola and utility provider Gas Natural were also reported to have suffered from the outbreak.

Britain's National Cyber Security Centre, part of the GCHQ spy agency, said it was aware of a cyber incident and was working with NHS Digital and the police to investigate.

Experts monitoring the situation have linked the infections to vulnerabilities released by a group known as The Shadow Brokers, which recently claimed to have dumped hacking tools stolen from the NSA.

A patch for the vulnerability was released by Microsoft in March, but many systems may not have had the update installed.