A massive cyber-attack using tools believed to have been stolen from the US National Security Agency (NSA) has struck organisations around the world.Cyber-security firm Avast said it had seen 75,000 cases of the ransomware – known as WannaCry and variants of that name – around the world.There are reports of infections in 99 countries, including Russia and China.Among the worst hit was the National Health Service (NHS) in England and Scotland.The BBC understands about 40 NHS organisations and some medical practices were hit, with operations and appointments cancelled.

How did the cyber-attack unfold?

The malware spread quickly on Friday, with medical staff in the UK reportedly seeing computers go down “one by one”.NHS staff shared screenshots of the WannaCry program, which demanded a payment of $300 (£230) in virtual currency Bitcoin to unlock the files for each computer.Throughout the day other, mainly European countries, reported infections.Some reports said Russia had seen more infections than any other single country. Domestic banks, the interior and health ministries, the state-owned Russian railway firm and the second largest mobile phone network were all reported to have been hit.Russia’s interior ministry said 1,000 of its computers had been infected but the virus was swiftly dealt with and no sensitive data was compromised.In Spain, a number of large firms – including telecoms giant Telefonica, power firm Iberdrola and utility provider Gas Natural – were also hit, with reports that staff at the firms were told to turn off their computers.People tweeted photos of affected computers including a local railway ticket machine in Germany and a university computer lab in Italy.France’s car-maker Renault, Portugal Telecom, the US delivery company FedEx and a local authority in Sweden were also affected.China has not officially commented on any attacks it may have suffered, but comments on social media said a university computer lab had been compromised.Coincidentally, finance ministers from the Group of Seven wealthiest countries have been meeting in Italy to discuss the threat of cyber-attacks on the global financial system.They are expected to release a statement later in which they pledge greater co-operation in the fight against cyber-crime, including spotting potential vulnerabilities and assessing security measures.