Anatomy of a hack and the anonymous hero who stopped it

As hospital after hospital went offline, security researchers around the world started poring over the ransomware that had gone round the globe.Despite the spread of the ransomware, researchers weren't impressed.Other researchers found that the malware was using Tor - anonymity software originally developed by US defence - to communicate with its command and control centre on the deep web (the part of the internet not visible to search engines).