This particular threat has been widely reported over the last several days, and frankly it warrants the attention of all Mac users.  Based on the nature of the ransomware encryption algorithm, it is quite possible that once infected, there will be no way to decrypt files, even if the bitcoin ransom is paid.  Be very careful when opening any files, especially those unexpected or from an unknown source.

https://threatpost.com/free-mac-based-ransomware-as-a-service-macransom-surfaces/126204/