Because browsers can host plug-in extensibility, security settings within the browser can make plug-ins fail. This is why in Internet Explorer 7 Data Execution Prevention (DEP) is off by default. When it is enabled many plug-in components fail to run, often crashing the browser.
You can enable DEP by navigating to the following dialog and checking the highlighted option shown below (note, you must elevated to admin first, otherwise the option is grayed out):
I have some great news, however.
Two of the most well-known and commonly used browser plug-ins, the Adobe Acrobat browser helper object and the Adobe Flash Player, now run when DEP is enabled.
So jump on over to the Adobe site, download the latest versions of Flash Player and Acrobat Reader, and enable DEP in IE7! I have!
A Big Thanks to the folks at Adobe for doing this.