It's happened to almost all of us at some point in our Web surfing experience -- you're visiting a new site when all of a sudden your screen begins to fill with boxes advertising goods and services from every corner of the Internet. Marketing firms claim that pop-up ads get more clicks than static advertising banners, though that could be due to user error rather than user intent. In other words, someone trying to close a pop-up ad might accidentally click on the ad link, giving the advertiser a false positive.

Before pop-up blockers, your entire screen could be overrun by ads like these. See more Web advertising images.

Some pop-up ads contain extensive animations or sound elements that can be distracting to surfers or even make it impossible to navigate through a Web page. Sometimes a user might prompt three more windows to open just as he manages to close the first one. Even worse, some pop-ups contain malicious code like spyware or computer viruses.



Most pop-up ads are Javascript applications that open a new browser window containing new content. The new window appears on top of your current view, obscuring the Web page you actually want to see. Because the ads are so intrusive, Internet users have consistently voted them the most annoying form of online advertisement in surveys.

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Enter the pop-up blocker. The earliest pop-up blockers appeared on the Internet scene in the mid '90s. The then-most popular blocker was PopUp Killer, created by Xavier Flix. Today, pop-up blockers come packaged in most Web browsers, and dozens of commercial and free programs also keep your browsing window clutter-free.

In this article, we'll look at what a pop-up blocker does, the different kinds of blockers you can use to reduce pop-ups and the potential issues you might encounter when you've activated a pop-up blocker.

Banners, Pop-unders and Floaters Banner ads used to be the standard form of advertisement on the Web. These ads are just hypertext links displayed in the form of an image. They may be static or they may incorporate Flash animation, but the purpose is always the same -- when you click on one, the link redirects your browser to the advertiser's Web page. Pop-unders are like pop-ups, except that instead of appearing on top of your browser window, a new window appears beneath your current browser. Normally you only notice pop-unders when you close your browser. Floaters (sometimes called Pop-overs) are also rising in popularity among advertisers. These are dynamic ads that can move across your screen as you look at a Web page.

A typical pop-up ad

Most pop-up ads are programmed in the Javascript programming language. When you click on a Web page that has pop-up ads, the ads activate as the page loads into your browser. The code for the pop-ups can be found within the code for the page itself. Pop-up blockers are programmed to scan a Web page's source code and search for any signs of a program telling your browser to open a new window. If the blocker finds this code, it deactivates the command and you don't get any pop-ups.
Not all pop-ups open when the Web page loads, though. Some activate when you click on a link or when you scroll your mouse over an activation site on the Web page. A good pop-up blocker can detect the code for these ads as well, though some are only able to deactivate a pop-up after it starts to open. If you've ever seen a pop-up quickly appear and disappear when you have a pop-up blocker activated, that's what happened. The blocker detected the ad after it activated, then disabled it.


Some pop-ups use other programming languages, such as Flash. A Javascript pop-up blocker is helpless against flash pop-ups because it's a completely different programming language. To block Flash ads, you'll need Flashblock program. These programs are similar to pop-up blockers in that they disable the commands found in Web pages that activate Flash animation. You can find programs that incorporate Javascript and flash ad blockers in one package.

But not all pop-up blockers are created equal. Some of them are very good at blocking nuisance pop-ups while leaving helpful pop-ups alone -- they're Intelligent pop-up blockers. In general, most intelligent pop-up blockers only disable pop-ups that open when a Web page first loads into your browser -- any pop-up that opens as a result of the user clicking on a link remains unhampered.

Trainable pop-up blockers rely on user input to determine which pop-ups to deactivate and which to leave alone. No two pop-up blocking programs are exactly alike, but in general the blocker asks the user if he wants to disable a particular pop-up when it first appears on the user's screen. If the user clicks on "Yes," then the blocker puts the offending pop-up on a black list, or a list of ads that should be deactivated in the future.
If you choose "No," the blocker puts the pop-up on a white list, which means it won't attempt to block the pop-up window again. While this kind of blocker is very easy to customize, it can become frustrating for the user as he makes choices for each and every pop-up. Also, if the advertiser alters the original pop-up in some way, it may slip past the blocker.

Serial pop-up blockers block every pop-up ad they're capable of uncovering. These blockers seek out every variation of the code used to generate pop-up ads and deactivate it whether the pop-up contains advertising or not. While these blockers usually ensure the user a pop-up-free experience, they can also cause complications when navigating through certain Web pages.

In the next section, we'll look at why you would want to disable a pop-up blocker.

What's All the Firefox Fuss About? In response to pop-up blockers, some site administrators have begun to include code in their site HTML that prevents their Web pages from appearing on the screens of Firefox users. Firefox has an ad blocking program built into the browser, which offends some Webmasters. If a Firefox user tries to visit such a Webmaster’s site, they will see a page of text explaining why they can’t view the Web page. The text accuses Mozilla (the publisher of Firefox) of infringing upon the Webmaster’s rights by blocking the advertising on his site. Enterprising Firefox users then look for ways to disable the protective code, whereupon the site administrator tries to find a new way to block them, and so it goes. As a counterpoint to the Webmasters’ argument, many users and designers of pop-up blocking programs argue that Webmasters have effective, less obtrusive advertising options at their disposal. Their point is that pop-up ads are so intrusive and distracting, they make surfing the Web an exercise of frustration. If Web pages featured less annoying advertising, there wouldn’t be a need for the blockers. Unfortunately, for some site administrators, pop-up ads are the best option due to their affordability and relatively high success rate.

So Why Do Companies Use Pop-ups?
That's a question a lot of companies are asking marketing firms. Pop-up blockers are very popular with Internet users -- one New Scientist poll said that up to 81 percent of Americans use some sort of pop-up blocker with their browser [source: New Scientist, December 16, 2006, Vol. 192, Issue 2582, p. 23]. Today, pop-ups aren't nearly the problem they were a few years ago. User surveys seem to suggest that a well-made video is less annoying than a pop-up. Unfortunately for advertisers, the ad considered to be the least annoying, the banner ad, is also the least effective. Users find banner ads to be the least intrusive, but they also hardly ever click on them.
Some companies still use pop-up ads because they're simple to set up and cheap to develop. If a company doesn't have a large advertising budget, pop-up ads might be tempting.