As annoying as popups are to your surfing experience, there are many popup blocker software solutions that are inexpensive and quite effective at preventing unwanted ads. Popup stopper software generally doesn't take up much disk space to slow down your computer, either.

Where do popups come from?
There are three main sources of popup (and pop-under) advertisements. The first and most common source is advertisements that are generated by the specific websites that you are visiting. Many websites try to enhance the revenue they receive by offering their own products or third-party products in popups.

The second-most-common source of popups is Internet Service Providers. Many ISPs will incorporate ads into the browsing experience of the users so that as people are surfing around the Internet, the user will see randomly generated popups. Of course, the ISPs do this to increase their revenue- unfortunately at the expense of their customers. Interestingly, some ISPs now offer popup stopper software as part of their service.

The third, and most insidious, source of popups is 'spyware' or 'adware'. Spyware and adware are related types of software that collect personal information about the user to pass along to advertisers and/or to create ads for that user. For example, if you have spyware or adware on your computer (spyware/adware can be installed on your computer without your knowledge by viruses or by knowingly installing or downloading a program onto your computer), this software will be tracking the websites that you like to visit. Let's say that you have been shopping for shoes recently; the spyware/adware will have tracked this and will now start delivering ads for shoes as you browse the Internet.

There is a fourth source of popup advertising becoming more popular recently, which is known as Messenger Service popups. Because they don't come through your browser, they are not usually technically considered a popup because they can spam you even 

when your web browser is closed. Many popup blocker software programs were not designed to block these types of popups.

Messenger Service popups will only be a problem for users with Windows 2000 or XP as their operating system. Microsoft incorporated this service (not to be confused with MSN Messenger, which is an Instant Messaging, or IM, program), so that network administrators could communicate to computers on their network.

For example, if the network administrator for XYZ Company wanted to remind everyone on their network to back up their data, they could do so by sending these messages to all the computers in the company. Messenger Service can be abused by spammers scanning for random IP addresses, so make sure to look for a popup blocker software program that can prevent these messages if they are truly unwanted.

The next section will discuss popup killers and how to make sure you pick the right popup blocker software for your needs.

What to look for in anti pop-up software?
The best way to prevent pop-up ads from interfering with your surfing experience is to purchase anti pop-up software. This software is fairly inexpensive (usually under $30), and there are some free versions out there as well. This is software that you purchase one-time and install on your computer. Some ISPs offer this anti-pop-up service as part of a bundle of services.

The first and most important thing to consider when purchasing pop-up blocker software is compatibility. Most pop-up blocker software will only work on some operating systems and only with some browsers. Make sure you check the system requirements when evaluating pop-up blockers.

Secondly, you want to make sure that the pop-up blocker will in fact block all sources of pop-up ads. Some pop-up blockers will only block certain types of pop-up ads, especially the free versions of the blockers. Also, make sure that if you have either Windows 2000 or Windows XP as your operating system, you find out if the pop-up blocker will prevent unwanted Messenger Service pop-ups.

Finally, you should find out if the pop-up blocker software you are considering allows for either blacklists, whitelists, or both. Sometimes sites communicate useful information via pop-up windows. The pop-up blocker can be told to remember these sites so pop-up windows are allowed to launch. This information is stored on your computer in what's known as a "whitelist" (as opposed to a "blacklist"). The pop-up blocker uses the whitelist to turn itself off when you visit sites whose pop-ups you don't mind viewing. For example, your bank's website might incorporate a pop-up as part of the sign-on process. You don't want this to be blocked all the time (requiring you to temporarily unblock it every time), so you can simply enter this site into your whitelist and the pop-up will come up every time.

In contrast to a whitelist, a blacklist will prevent any pop-ups from specific sites that you enter on the list. For example, if there is a certain news site that you go to all the time that has a pop-up as soon as you hit the site, you can permanently disable this site so that no pop-ups will ever be generated.

In summary, most pop-up blockers work very well in doing the job that they were designed to do. Just make sure that whatever solution you implement has the criteria that is important to you.