According to Microsoft Download Page for .NET Framework 3.5 SP1, I should install KB959209 and KB967190 immediately after installing the .NET Framework package:
IMPORTANT: After installing the .NET Framework 3.5 SP1 package (either the bootstrapper or the full package) you should immediately install the update KB959209 to address a set of known application compatibility issues. In addition, on Windows Vista x64 and Windows Server 2008 x64, install the update KB967190 to address a file association issue for XPS documents.
I handle the installation of the .NET Framework in my installer (Inno Setup). So how do I detect if those two hotfixes are installed, so I can decide whether to download them and install them? I don t want to bother the user with unnecessary steps, so as automatic and passive solution as possible is preferred.