What Causes Internet Pop-Up Ads?

By John Grossman

Internet pop-up ads are new windows that your browser opens when you click on a link or load a Web page. While some pop-up ads serve a legitimate purpose, most of them only contain advertisements. It is possible to get rid of pop-up ads using your browser's integrated pop-up blocker.


There are two different types of pop ads: pop-up ads and pop-under ads. Pop-up ads force your browser to open a new window or a new tab when you click on a link or when you load or quit a certain Web page. The new window or tab then becomes the new active page and your browser displays it on top of the page you actually wanted to visit in the first place. A pop-under ad works the same way, except that your browser loads it under the page you want to visit. The pop-under ad can only become visible when you quit the page you wanted to visit.


Pop-up and pop-under ads are typically used for advertising. While some websites do use pop-up ads for legitimate purposes, such as to remind you of an important new feature, other websites use pop-up and pop-under ads as a way to maximize their ad revenues by presenting their readers with additional advertisement. Another use for pop-up and pop-under ads is phishing. Phishing refers to the practice of trying to acquire sensitive information such as your passwords, your personal details or your credit card number by using malicious means. Such pop-up ads may, for example, use your webmail provider's logo to try to make you input your login details, therefore gaining access to your email account.


Pop-up and pop-under ads usually use a technology called JavaScript. Web developers routinely use JavaScript to create more interactive pages than the ones they can create using simple HyperText Markup Language, or HTML. JavaScript provides a few features that allow developers to create pop-up and pop-under windows. One of those features, for example, is the "onClick()" function. Web programmers can use that function to make your browser perform a certain action when you click on a link, such as opening a pop-up ad.


The recent versions of most Internet browsers, such as Mozilla Firefox, Microsoft Internet Explorer or Google Chrome, have an integrated pop-up blocker. You can usually enable that feature in the "Options" menu of your browser. Those pop-up blockers do not eliminate 100 percent of pop-up and pop-under ads. Web developers are constantly trying to find new ways to evade the pop-up blockers and they can sometimes create pop-ups that your browser is not able to detect.