What is WannaCry ransomware and why is it attacking global computers?

Malicious software has attacked Britain’s health service and companies in Spain, Russia, the Ukraine and Taiwan. What is it and how is it holding data to ransom?WannaCry malicious software has hit Britain’s National Health Service, 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 revealed to the public as