You should only load custom Start Page XAML files from a trustworthy source. The XAML file {0} may have come from a location ...

You should only load custom Start Page XAML files from a trustworthy source.  The XAML file {0} may have come from a location that isn't fully trusted.  It could present a security risk to your computer because the page and any referenced assemblies will run under the privileges of the current user.