Microsoft Security Essentials is free. I've never been infected, with it running on all our computers. When I went to an 8.1 OS, it changed names to Microsoft Defender. Again, free.
F-Fred, like any Virus protection program, you have got to let them download the daily virus file. You can set this up to happen anytime of day. Since our computers run 24 hours a day, we set then up to download the new virus files at 2:00am.