You could log data about the user (example by captaincrunch in their updated comment), directly modify the way the page looks (e.g. a fake virus alert page) or

You could log data about the user (example by captaincrunch in their updated comment), directly modify the way the page looks (e.g. a fake virus alert page) or simply redirect the user to any site you want. It's bad on a 'normal' site, but even worse here given their target market.