If you update via the application or allow it to update on its own, Grime Fighter gets installed whether you wanted it or not, you don't get a choice, which is a complete crock of crap. Why is Avast! installing stuff unrelated to a simple application update? It's as bad as an application installing Google Chrome, Google Toolbar, Ask.com Toolbar or any other extraneous garbage that we didn't bargain for, without our knowledge or consent. If we download and install, we're presented with a choice to opt out of the extra garbage, but with an update via the application (whether manual or automatic) that choice has been taken away from us. What a crock!
In this case, our only choice is to go to Add/Remove Programs (Programs and Features in Vista/7), opt to Change the installation, uncheck Grime Fighter, click Continue, and get rid of it.