An infected version of Transmission BitTorrent cliet (2.90) has been seen in the wild (on the Transmission home page). The authors recommend people upgrade to version 2.92 ASAP.

The current version encrypts the users files and holds them to ransom, but it looks like a work-in-progress. There are hooks in the program to also encrypt TimeMachine backups, which would mean that the user can't even restore from a backup, once they have cleaned their system ,but it isn't currently implemented!

http://www.zdnet.com/article/new-os-x-r ... RSSbaffb68