I don't run anything other than what windows includes in terms of antivirus.  Used to run Norton but gave it up after multiple problems with it interfering with other programs.

I will reiterate that taking my PC offline when starting QB is still working perfectly.  I have been testing it periodically all morning after having a lot of trouble getting it to start earlier.  I know it isn't a perfect answer but if it works it's better than pulling your hair out.