New York--Pop-under ads, which are online ads that launch a new browser, are effective in building brand awareness but fail to convert browsers to buyers, Jupiter Media Metrix Inc. reports in a new study. In the report, Jupiter examined a pop-under ad campaign launched by wireless camera site X10.com, which reached 32.8% of the Web audience between January and May. While the campaign was successful in reaching a mass audience, it did not hold users at the site, Jupiter reported. The research company found that 73% of unique visitors left the site or the window before 20 seconds after viewing or clicking on the pop-under ad. Jupiter cautions marketers to carefully consider pop-uunder campaigns, because it is a strategy dependent on cheap and limitless inventory. Other sites deploying pop-under ads include Half.com, Real.com and Colonize.com.