Well, after a couple minutes of looking... I believe it is an update for Visual Studio 2008 or .NET 3.5 relating to WPF. I also believe the Visual Studio installer is what installed it on me. This is just a guess based on this web page:
http://blogs.msdn.com/usisvde/archive/2007/08/13/resolution-wpf-stops-working-with-vs-2008-beta-2.aspx
Chris