Internet Explorer 8 provides a great deal of additional features and security as compared to its predecessors. These features are so great in fact, that Microsoft is now pushing IE8 as a high-priority update through Windows Update.
Although the enhancements of IE8 are great, the browser has also changed the way it interprets certain website code. Because of this, you may notice several websites not appearing or functioning properly in IE8. Companies highly dependent upon custom web applications or intranets may find that IE8 leaves these applications unusable. In response to this, Microsoft has released the IE8 Blocker Tool to block the installation of the browser upgrade on your organizations PC’s until these compatibility issues can be resolved.
This tool will block machines in a network from installing Internet Explorer 8 as a high priority update, and will cause it to be listed under optional updates on the Windows Update website. You can download the IE8 Blocker Tool here: http://www.microsoft.com/downloads/details.aspx?FamilyID=21687628-5806-4ba6-9e4e-8e224ec6dd8c&displaylang=en.