From what I understand, both viruses have been seen on all versions of Windows, even 7.
Normally it gets there by popping up a fake virus warning window, with a button to click to "clean now" or "scan now". It looks very much like a Windows Defender window and sometimes mimicks other popular anti-virus programs. The one that got us, my wife clicked on a pop-up that looked almost exactly like a norton window, and since we had norton at the time, she clicked "scan now" and it was all over for that computer. Another very insidious thing it does is block other AV programs and will not allow them to run or to be installed. It can even do this in safe mode. Seriously destructive viruses.