The WannaCry ransomware is bad news. It is known to spread like a worm over the LAN once a machine is infected. Microsoft is urging everyone to install critical patches immediately.
WannaCry is ransomware and starts out in the traditional fashion: a fraudulent email with a link or attachment. But WannaCry is different in that is can spread to unpatched machines inside the network on its own. This is what makes the impact so high as the number of computers affected worldwide is estimated at 200,000.
Like all other ransomware, the list to protect yourself is pretty simple:
Here are some articles for more information:
https://blog.knowbe4.com/ransomware-attack-uses-nsa-0-day-exploits-to-go-on-worldwide-rampage
https://redmondmag.com/articles/2017/05/12/ransomware-outbreak-targeting-windows-smb-flaw.aspx