I bought your magazine to find out if I had the best free antivirus. In the past I bought such a program, but to upgrade I needed to upgrade my computer. I will not buy that again. So, I read your review and thought OK Avira comes out well. So I tried to install it. No joy. Then I tried Bitdefender - same thing. I am wary of Qihoo. I have a PC running under Windows 10 and am currently using AVG. Why can't I install the other two?