Jefferson Fletcher: The IE Automatic Component Activation (IE ACA) update is now available as part of the April 2008 Internet Explorer Cumulative Update. The "click to activate" behavior, formerly required for ActiveX controls embedded in some webpages, is now permanently removed from Internet Explorer. For detailed information on IE ACA, see our blog post from last November announcing this update.
This update replaces the IE ACA previews released in December 2007 and February 2008.
News Source: IE Blog