Palo Alto Networks claims to have discovered the first known instance of OS X Ransomware in the wild, called “KeRanger” KeRanger attacks Apple’s Macintosh computers and demands payment of $410 in Bitcoin. Malware encrypts the important documents and files on infected machines and then asks victims to pay ransoms in digital currencies so they can regain access to their data. It is still unclear how the hackers managed to compromise the Transmission app and upload the infected files. If the malware is widespread, it could affect other common Mac apps as well.
Source: https://thehackernews.com/2016/03/mac-os-x-ransomware.html