Allows an assembly to be called by partially trusted code. Without this declaration, only fully trusted callers are able to use the assembly. This class cannot be inherited.
The net_v40_long introduces new security rules that affect the behavior of the System.Security.AllowPartiallyTrustedCallersAttribute attribute (see Security-Transparent Code, Level 2). In the net_v40_short, all code defaults to security-transparent, that is, partially trusted. However, you can annotate individual types and members to assign them other transparency attributes. For this and other security changes, see Security Changes in the .NET Framework Version 4.
.NET Framework version 2.0 (level 1 transparent) assemblies must be strong-named to effectively use the System.Security.AllowPartiallyTrustedCallersAttribute (APTCA) attribute. net_v40_short (level 2) assemblies do not have to be strong-named for the APTCA attribute to be effective, and they can contain transparent, security-critical and security-safe-critical code. For more information about applying attributes at the assembly level, see Applying Attributes.
By default, if a strong-named, level 1 transparent assembly does not explicitly apply this attribute at the assembly level, it can be called only by other assemblies that are granted full trust. This restriction is enforced by placing a System.Security.Permissions.SecurityAction.LinkDemand for FullTrust on every public or protected method on every publicly accessible class in the assembly. Assemblies that are intended to be called by partially trusted code can declare their intent through the use of System.Security.AllowPartiallyTrustedCallersAttribute. An example of the declaration in C# is [assembly:AllowPartiallyTrustedCallers]; an example in Visual Basic is <assembly:AllowPartiallyTrustedCallers>.
The presence of this assembly-level attribute prevents the default behavior of placing FullTrust System.Security.Permissions.SecurityAction.LinkDemand security checks, and makes the assembly callable from any other (partially or fully trusted) assembly.
When the APTCA attribute is present, all other security checks function as intended, including any class-level or method-level declarative security attributes that are present. This attribute blocks only the implicit, fully trusted caller demand.
For more information, see Using Libraries from Partially Trusted Code.