ActiveX is the mechanism by which Internet Explorer (IE) loads other applications in the browser. Through ActiveX, IE loads Windows Media Player, Flash, Quicktime, and other applications that can read files embedded in web pages. ActiveX controls are activated when you click an item such as a .WMV file on a web page to download it for display in your Internet Explorer browser window.

• As a Microsoft product, ActiveX was specifically designed to work with Windows systems. ActiveX is not supported by Microsoft on other operating systems such as Mac or Linux.

Firefox and other browsers that work on multiple operating systems use the Netscape Plugin Application Programming Interface (NPAPI) system. NPAPI performs functions similar to those of ActiveX.

Note: Firefox does not officially support ActiveX.

Background on ActiveX

ActiveX was designed to make seamless media playback through Internet Explorer easier. When you select media on a web page, Internet Explorer downloads the content and calls the appropriate ActiveX control, as requested by the web page, to load the playback application in the browser, potentially with little or no involvement, by you.

• Because this system is capable of automatically downloading new ActiveX controls without your involvement, it has been exploited by spyware, viruses, and other malicious software. Internet Explorer has improved ActiveX security in a number of ways, and many of the security loopholes have been closed in IE 7. However, it is still relatively easy to download and activate a malicious ActiveX control on your computer.

An ActiveX control is the equivalent of an NPAPI plugin. However, ActiveX and plugin technology have differences. While the potential effects of malicious content are similar, plugins inherently have better security features. Plugins have less control over the web page in which they are embedded and cannot be used in applications other than a web browser. ActiveX has broader use across a greater number of applications.