When you install a hotfix that updates any Microsoft .NET Framework component on a computer running Microsoft Windows 2003 or earlier, the patched component will trigger a repair of the entire .NET feature set. When the feature set is repaired, it will repair all sub-features and their dependencies as well. Since Microsoft ASP.NET is part of the .NET Framework feature set, a feature set repair for the updated .NET framework component will trigger all of the custom actions associated with an ASP.NET feature repair as well. Even if the .NET hotfix does not directly update an ASP.NET component, it will still trigger a repair of the ASP.NET feature set.
During an ASP.NET feature set repair routine, the servicing simply calls aspnet_regiis.exe with "-iru" parameters. This routine performs a number of checks and takes certain actions that could possibly change the ASP.NET configuration under very rare circumstances. As mentioned above, this routine will run even if no ASP.NET components are getting updated by the hotfix, and therefore also has the potential to alter some ASP.NET configuration settings. Installation of such a hotfix will also trigger IIS and ASP.NET application domain restarts.
Microsoft recommends that you backup your IIS and ASP.NET configuration files before installing any hotfix that updates Microsoft .NET Framework components.
Prior to Microsoft .NET Framework 4.0, the ASP.NET feature set was always installed as part of .NET Framework feature set. Starting with Microsoft .NET Framework 4.0, ASP.NET does not take feature set dependencies from the .NET framework, and therefore the issue described in this article does not apply to Microsoft .NET Framework 4.0 servicing.
Microsoft .NET Framework 1.0, Microsoft .NET Framework 1.0 Service Pack 3, Microsoft .NET Framework 1.1, Microsoft .NET Framework 1.1 Service Pack 1, Microsoft .NET Framework 2.0, Microsoft .NET Framework 2.0 IA64 Edition, Microsoft .NET Framework 2.0 Service Pack 1 (x86), Microsoft .NET Framework 2.0 Service Pack 2, Microsoft .NET Framework 2.0 x64 Edition, Microsoft .NET Framework 3.0, Microsoft .NET Framework 3.0 Service Pack 1, Microsoft .NET Framework 3.0 Service Pack 2, Microsoft .NET Framework 3.5, Microsoft .NET Framework 3.5 Service Pack 1, Microsoft ASP.NET 1.1, Microsoft ASP.NET 1.0, Microsoft ASP.NET 2.0, Microsoft ASP.NET 3.5