Essential .NET, Volume 1: The Common Language Runtime

Policy

Evidence by itself is relatively useless. Rather, the raison d'être for evidence is to act as input to a security policy. The CLR uses security policy to determine what permissions to assign to a given assembly based on the assembly's evidence. System administrators and users can configure CLR security policy. The CLR security policy is also extensible, allowing one to plug in custom policy algorithms to the existing infrastructure.

One can specify security policy at up to four levels, which are represented by the System.Security.PolicyLevelType enumeration:

namespace System.Security {
  public enum PolicyLevelType {
    User,
    Machine,
    Enterprise,
    AppDomain
  }
}

The User policy level is specific to an individual user, whereas the Machine policy ...