This is done to prevent malware faking the prompt and/or user consent. And it's ...

		jimbobimbo on June 26, 2011 \| parent \| context \| favorite \| on: OS X – Safe, yet horribly insecure This is done to prevent malware faking the prompt and/or user consent. And it's not just "blacking out the display" - the whole thing is executed on another desktop (in OS terms, not in user terms): http://blogs.msdn.com/b/uac/archive/2006/05/03/589561.aspx