Nope Windows 7 Ulti.
seriously guys, if you know what you are doing (which a lot of MyBB users do), you don't need that anti virus junk.
Unless you disable all scripting and most functions in your browser you do know its possible to exploit browsers to automatically run 0 day exploits? What it does it when your browser visits the website, it injects a payload. Since you have no AV then the injection will go unnoticed. If you wanna I can see if you are vulnerable tomorrow? Setup a website, ask you to browse to it and see what happens?
When I tested SET and Armitage on local VMs, I was able to root the boxes running no AV, but the up to date VMs running AVs picked up and blocked my payload.