VB.NET:

Imports System.Security.Permissions
Imports System.IO<Assembly: UIPermission(SecurityAction.RequestOptional, _
Unrestricted:=True)> 
<Assembly: FileIOPermissionAttribute(SecurityAction.RequestOptional, _
Read:="C:\")> 
<Assembly: FileIOPermissionAttribute(SecurityAction.RequestRefuse, _
Read:="C:\Windows\")> 
Module Module1Sub Main()
        Console.WriteLine("Reading one line of the boot.ini file:")
        Dim sr As StreamReader = New StreamReader("C:\boot.ini")
        Console.WriteLine("First line of boot.ini: " + sr.ReadLine)
    End Sub

End Module 

C#:

 using System;

using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.Permissions;
using System.IO;

[assembly: UIPermission(SecurityAction.RequestOptional, Unrestricted 

RequestMinimum contains permissions must have, RequestOptional contains permissions might use and reject all that are not listed, and RequestRefuse reject all permissions listed.