You've probably heard about the the latest outbreak of the 'Petya' ransomware. Like WannaCry, this is a worm-enabled ransomware, so it can spread across your network to infect other machines. It sounds like 'Petya' not only encrypts files, but also uses mimikatz to steal administrative credentials as well.
Links are below to more information, but here are the quick hitters:
Krebs: https://krebsonsecurity.com/2017/06/petya-ransomware-outbreak-goes-global/
The Register: https://www.theregister.co.uk/2017/06/28/petya_notpetya_ransomware/