I think dad has Mountain Lion (I'd have to look). He tried Maverick- hated it. Both he and my brother (one of the other 2 Mac fans) are leery of Yosemite. Not sure what niece thinks of Yosemite or what she has.
In the article above it says that the average Mac user will not get hit by that particular virus because it's so difficult to exploit- most hackers will set their sights a lot higher.