What is 'WanaCrypt0r 2.0' ransomware and why is it attacking the NHS?

Malicious software has attacked computers across the NHS and companies in Spain, Russia, the Ukraine and Taiwan. What is it and how is it holding data to ransom?Global cyber-attack – live updates
‘WanaCrypt0r 2.0’ malicious software has hit the NHS, some of Spain’s largest companies including Telefónica, as well as computers across Russia, the Ukraine and Taiwan, leading to PCs and data being locked up and held for ransom.The ransomware uses a vulnerability first r