Commercial web sites make efforts to ensure that the ads they run are not going to screw up their users. Yahoo’s banner ad and JavaScript banner guidelines state: “Advertisements cannot mislead the user. For example, they may not mimic or resemble Windows/Macintosh/Unix dialogue boxes, error messages, or the like” and “banners may not contain graphics that simulate interactivity (ie drop down menus, search boxes and the like) without that functionality truly existing.” They also imply that they test all the ads, which makes complete sense. The ads are, in a sense, becoming part of their site, and therefore should conform to their standards of user interaction and quality. Lycos’ guidelines are similar.