Pop-ups and pop-unders are types of Web browser windows that open up and appear automatically without you explicitly giving them permission to do so. These windows open on a number of different sites, including sites that are supposed to be trustworthy. Many Web browsers have built-in pop-up blockers that can automatically delete pop-ups and pop-unders as they appear on your screen. You can learn how to enable this feature in just a few steps.
Start Internet Explorer.
Click the "Tools" menu option at top of the screen, then hover over "Pop-Up Blocker."
Click "Turn on Pop-up Blocker." This starts the pop-up blocker, which automatically deletes pop-ups and pop-unders as they appear.
Start the Google Chrome browser.
Click the wrench icon at the top-right corner of the screen to open the settings drop-down menu, then click "Options."
Open the "Under the Hood" tab and click the "Content Settings..." button.
Select the radio box in the Pop-ups section next to, "Do not allow any site to show pop-ups (recommended)."
Click "x" to close the "Options" tab.
Start Firefox, click "Tools" in the menu bar and then click "Options."
Open the "Content" tab and check the box next to, "Block pop-up windows."
Click "OK" to save your changes.