PopUp / PopUnder advertisement
Unlike pop-up windows that load over your web page, pop-under windows quietly load under your web page. Your visitors probably won't even see the pop-under window until they're finished at your site and close the window .
The effectiveness of pop-under windows most likely stems from the timing. When your visitor first enters your site, their mind is on what lead them to your site to begin with. Pop-up windows will most likely cause a higher percentage of your visitors to instantly close your window before viewing its content. That's what makes pop-under windows more effective -- your visitor is through visiting your site and their mind is clearer. They will be much more likely to take the time to look at your offer when they don't have another objective on their mind .