The Redmond, Wash.-based software giant recently indicated that it will add pop-up blocking features to Internet Explorer (IE) next year, as part of an update for Windows XP. Others have offered similar tools before, but because IE so thoroughly dominates the browser market, ad executives and Internet watchers believe the changes could finally burst the bubble for pop-ups. "If Microsoft does it right," said Richard Smith, a well-known security and privacy expert, "I think we will see a big drop in the use of pop-ups." Fearing that they might lose one of their most effective advertising tools, some publishers and advertisers are developing methods to get around pop-up blockers and still deliver their ads. But rather than fight, many advertisers that have come to rely on pop-ups are bracing for a sea change that could force them to abandon one of their most effective marketing formats. Pop-up advertisements came into vogue during the Internet bust, when online advertising couldn't bring home the bacon for Net publishers. Publishers could serve as many pop-up windows as they wanted for pennies because they didn't take up any room on the page. There was an economic incentive to peddle more ads, too, because marketers paid based on how often Web surfers responded to their pitches, or what's called "customer conversions." The more conversions, the more ad dollars. As a result, marketers were drawn to pop-ups because they're economical and effective--they grab Web surfers' attention like no other online ad. Pop-ups are 13 times more effective than banner ads that run the length of a page, according to research from Advertising.com published earlier this year. More on ZDNet