Figure 4. The IIS 6.0 Compatibility Architecture. IIS 6.0 includes the IIS 5.0 Isolation Mode, which makes it behave like IIS 5.0. This means that applications can run in any of the three IIS 5.0 application modes. This also means that when you run IIS 6.0 in this mode, you'll be facing the same security impacts as if you were running IIS 5.0.