How to set ACL (Access Control List) properties on a folder programmatically

Some folders do not permit access. Here is how to set ACL's programatically.

using System.Security.AccessControl;

        public static void setAccessRule ( string directory )
        {
           System.Security.AccessControl.DirectorySecurity sec = System.IO.Directory.GetAccessControl ( directory );
           FileSystemAccessRule accRule = new FileSystemAccessRule ( Environment.UserDomainName + "\\" + Environment.UserName,
                  FileSystemRights.FullControl, AccessControlType.Allow );
            sec.AddAccessRule ( accRule );    // setACL
        }