Pop-up ads are a form of online advertising on the World Wide Web intended to increase web traffic or capture email addresses. It works when certain web sites open a new web browser window to display advertisements. The pop-up window containing an advertisement is usually generated by JavaScript, but can be generated by other means as well.
A variation on the pop-up window is the pop-under advertisement. This opens a new browser window, behind the active window. Pop-unders interrupt the user less, but are not seen until the desired windows are closed, making it more difficult for the user to determine which Web site opened them.
For early advertising-supported web sites, banner ads were sufficient revenue generators, but in the wake of the dot com crash, prices paid for banner advertising clickthroughs decreased and many vendors began to investigate more effective advertising methods. Pop-up ads by their nature are difficult to ignore or overlook, and are claimed to be more effective than static banner ads. Pop-ups have a much higher click rate than web banner ads do (about every 14,000th popup ad is clicked on).
Pornographic web sites are among the most...