I have been running tests on the use of Pop-Unders to promote several types of products and services. Note that I am discussing POP-UNDER'S... not Pop-UP's. I consider Pop-Up's too intrusive. Pop-Under's on the other hand load in the background when visiting a site and, therefore, are not perceived in the same way as the much more intrusive Pop-Up.To source vendors of Pop-Under advertising go to Google and search on "Pop Under Advertising". You will find dozens of vendors selling Pop-Under tr.