// (c) 2006 Richard Grimes
// www.grimes.demon.co.uk

using System;
using System.IO;
using System.Security.AccessControl;
using System.Security.Principal;

class App
{
   static void Main()
   {
      DirectoryInfo di = new DirectoryInfo("Test");
      DirectorySecurity ds = di.GetAccessControl();
      FileSystemAccessRule fsar = new FileSystemAccessRule(
         new NTAccount(@"BUILTIN\Users"), FileSystemRights.Write, AccessControlType.Allow);
      ds.AddAccessRule(fsar);
      di.SetAccessControl(ds);
   }
}