Start > Run > msconfig > Startup tab > find whatever the hell process you're looking for > uncheck > reboot
or services tab, i dunno.
i think the process for your anti-virus starts up when you boot your computer, so even if you do disable it (in the tray) it still runs in the background since its in a way "locked" as a startup process.
if you disable it in msconfig, but it still doesn't work, REMEMBER TO REACTIVATE IT.
also pray your firewall will keep you safe in this moment of testing.
