sorry got cut off, all you have to do is replace the
http://aa with whatever url you want to re-direct the 'scumware' user to it then sends them to that url instead of your site i use it to send them to a page that says:
'you are using scumware that replaces our ads with the software makers own! please un-install _______ and come back thank you'
This way you can potentially get that surfer back, but if you don't they aren't wasting your content and bandwidth.