MaximumPC wrote an interesting article proving that Apple users now need to worry about these ransomware viruses.
For those that don't know; these viruses encrypt your files so you can not access them. They then demand money for your files back. Worst part it's usually in bitcoin so it's not possible to have a paper trail.
Easiest way to avoid this grief is to have a proper backup that is not connected to your computer. If there is a drive letter the virus can encrypt the files so it's important to have an unattached backup.
Be safe guys!