Check out this article:
http://blogs.msdn.com/b/ieinternals/archive/2011/03/22/authenticode-code-signing-for-developers-for-file-downloads-building-smartscreen-application-reputation.aspx (http://blogs.msdn.com/b/ieinternals/archive/2011/03/22/authenticode-code-signing-for-developers-for-file-downloads-building-smartscreen-application-reputation.aspx)
http://www.jeff.wilcox.name/2010/02/codesigning101/ (http://www.jeff.wilcox.name/2010/02/codesigning101/)