In the beginning, advertisers relied on banner ads strategically placed around a web page. However, they found that people routinely ignored them, so to force people to at least acknowledge the advertisement's existence, they created pop-up and pop-under ads.
Pop-up ads blanket your screen with windows, advertising anything from lower mortgage rates to vacation trip giveaways (see Figure 17-4). Since these windows cover any web page you're currently browsing, you can't see anything until you close the pop-up ad window. Pornography advertisers have created particularly annoying pop-up ads that spawn three or four more pop-up windows every time you close one.
Pop-under ads are a bit more subtle. They also appear in little windows all over your screen, but they hide under your currently displayed web page, so you won't even see them. The moment you close your browser, though, those pop-under ads seem to magically appear, cluttering up your screen. Since pop-under ads don't intrude upon your browsing activities, advertisers hope that more people will be more receptive to them.
Even if you decide to opt-out from DoubleClick's ads, you may still find yourself bombarded by pop-up and pop-under advertisements. To learn how to stop pop-up and pop-under ads from wrecking your Internet experience, visit the Web Ad Blocking site (http://www.ecst.csuchico.edu/~atman/spam/adblock.shtml).
If you want to automatically block pop-up and pop-under ads from appearing, you'll need to get a pop-up blocker program. Go to WebAttack.com (http://www.webattack.com) or Tucows (http://www.tucows.com) and search for "pop-up blocker." Both sites offer plenty of free and shareware pop-up ad blockers, such as the one shown in Figure 17-5, and you can try to find the one you like best.
For a free way to block pop-up ads, stop using Internet Explorer or Netscape and grab a copy of Mozilla (http://www.mozilla.org) or Safari (http://www.apple.com). Both browsers offer commands that let you block pop-up ads from appearing and disturbing your web surfing experience.