Many browsers and browser toolbars have a pop-up blockers built in. Several sites and Internet service providers also have pop-up blocking capabilities. Depending on how ads are served, these pop-up blockers can cause problems in reporting of impressions.
All pop-up and pop-under ads use JavaScript to create the new window. For the most part, pop-up blockers intercept this JavaScript function and prevent the new window from being displayed. Usually, ads count an impression when the ad tag is called rather than when the pop-up window is displayed. As a result, with regular ads, an impression will be counted even though the pop-up window has not been shown. The interstitial creative type prevents this counting problem. With an interstitial creative, no impression is counted when the ad tags are called. Instead, the impression is counted when the browser requests the image in the pop-up ad.
For example, a pop-up creative might look something like this:
<script language="JavaScript">
var ad_code = '<html><head><title>Pop-up Ad</title></head>';
ad_code += '<body marginheight=0 marginwidth=0 leftmargin=0 topmargin=0>';
ad_code += '<a href="%chttp://www.clickthrough.com"><img src="%h/12345/image.gif"></a>';
ad_code += '</body></html>';
pop = window.open('','',"height=200,width=200");
pop.document.open()
pop.document.write(ad_code);
pop.document.close()
</script>
This creative would be served through a Rich Media tag, either Iframe or JavaScript. The browser will request the ad through the ad tag. The ad server will send the ad code and count an impression. The pop-up blocking software or browser will prevent the pop-up window from being displayed. With a regular creative, the impression is counted when the custom creative code is sent. As a result, an impression will be counted even though the pop-up ad was not displayed.
When interstitial creative is used, the ad server counts an impression when an image or other file in the custom creative code is retrieved. The %i macro is used to designate which image or file will be used for counting an impression. For example, using the above pop-up code sample, the image source URL would have %i inserted in front of it:
ad_code += '<a href="%chttp://www.clickthrough.com"><img src="%i%h/12345/image.gif"></a>';
The creative would be trafficked as an interstitial, and the tags would have to be enabled to serve an interstitial creative. The ad server would send the code for the interstitial creative and not count an impression.
Without pop-up blocking software, the browser would launch the pop-up window. The browser would retrieve the contents of the pop-up window, including the image file with %i. When the browser requests the image file with %i, the ad server will count an impression.
When the browser has a pop-up blocker, the browser or pop-up blocking software would prevent the pop-up window from opening. As a result, the image is never retrieved, and the ad server does not count an impression.