I am using Windows Vista and wanted to uninstall Avast! antivirus before trying an alternative software. After trying to uninstall Avast! the standard way, that is through Windows' uninstall dialog and rebooting the PC twice, Avast! was still showing in the system tray, so I checked the offline help, which mentioned an uninstall utility but leads to a broken web link. So I went to Avast website and finally found the uinstall utility available for download here.