So there is finally a potentially dangerous malware out there for Macs. It is attached to the back of a program called Transmission, which is used to download torrent on file sharing websites.
It is only attached the Transmission 2.90. If you use Transmission and want to check what version you have, open Transmission, then up next to the Apple, click Transmission, then click About Transmission. Here it will tell if what the version is.
If you have version 2.90, then head straight to the Applications folder in Finder and delete it.
You can then google Transmission 2.92 and download it. This version is clean.
On the other hand, if you have got the latest version of Apple's OS, El Capitan, then your much less at risk, as it has a built in checking system the knows if you've got the dodgy version of Transmission.
Best to keep things up to date. Always.