Some pop-up windows ask you to download activeX to view Web site content.

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It's happened to all of us. You're surfing the Web, having a great time, learning things you never knew, meeting people you'll never "meet," watching videos and playing games, when suddenly a pop-up window appears.

It says that you need to download this thing called "ActiveX" to view the content on this Web site. Active what? You read somewhere that you should never download anything from the Internet that you don't recognize, so now you're stuck. Do you skip the site or do you take a gamble on ActiveX?

In most cases ActiveX is harmless. In fact, it can even be incredibly helpful. In Internet Explorer, ActiveX technology allows you to play video clips directly in the browser window. It's what allows you to watch Web animation and read .PDF files without opening up another application.

But ActiveX has also received more than its share of bad press. Over the years, hackers have disguised malicious programs and viruses as innocent ActiveX downloads. For the average computer user, one ActiveX download prompt looks just like another. The result can be a hard drive infected with spyware, adware and even infectious worms.

So what is ActiveX exactly? How can it be used for playing Flash movies and animated GIFs on Web pages? And what are some things you can do to protect yourself against ActiveX security threats? Read on to find out.