Question - What is FullTrust? Do GAC’ed assemblies have FullTrust?
Answer -
Before the .NET Framework existed, Windows had two levels of trust for downloaded code. This old model was a binary trust model. You only had two choices: Full Trust, and No Trust. The code could either do anything you could do, or it wouldn't run at all.
The permission sets in .NET include FullTrust, SkipVerification, Execution, Nothing, LocalIntranet, Internet and Everything. Full Trust Grants unrestricted permissions to system resources. Fully trusted code run by a normal, nonprivileged user cannot do administrative tasks