We use Eset on the few windows machines we have. Checkout the graph on this page on their website if you think your free AV software is really getting rid of all the virus'

I am not use any Anti-virus because of my Hard Disk status is Read Only.

When I open my PC then I allow to do anything but when I turnoff my PC then my all save change will be lost... and again when I start my PC then everything is fresh and new..