I believe I got hit by this about a week ago when I clicked on an advert linked on Chicago Tribune's website.
A fullscreen message appeared saying my computer had been encrypted and I had to pay $300 to decrypt it. I pulled my network cable out and had to power off my PC because the keyboard would not work. I was able to boot back up, but when I logged in both regularly and in Safe-Mode, a full white screen saying "please connect to the Internet" appeared and I couldn't use the keyboard again.
I pressed F8 on boot and booted into Safe-Mode Command line only. Once I logged in and saw the command line, I typed rstrui.exe (windows System Recovery) and using the Restore Wizard, restored to a checkpoint from a day earlier. I restarted my PC again and let it boot normally and once I was able to log in without seeing the message, reconnected my network cable.
My PC was never encrypted. The message only said it was. The clincher was before I booted Windows in Safe-Mode, I used a Knoppix DVD to mount the Windows partition and copy off my personal data before I started the recovery process. The data was perfectly readable and not encrypted.