Ok, So I'm a former Cybersecurity specialist from the largest Telco in Australia, Telstra.
An example:
The initial attack vector for the WanaCrypt0r is unknown, it is certain that the spread of the ransomware occurs through exploitation of the ETERNALBLUE vulnerability (CVE-2017-0144) in Microsoft Windows. Patches for this vulnerability for all supported versions of Windows have been available since March 2017. On Friday May 12, 2017, Microsoft took the seemingly extraordinary step of releasing patches for out-of-support versions of Windows to help protect against these attacks.