CodeIgniter基本控制器扩展

我想自己扩展基本控制器。这是我放在application/libraries 中的文件MY_Secure.php的代码

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
Class MY_Secure extends CI_Controller {
  public function __construct() {
    parent::__construct();
    if(!$this->session->userdata('status') == 'admin') {
        $data['message'] = '<p class="error">You shold login in admin area</p>';
        $this->load->view('admin/login', $data);
    }
  }
}
?>

这是我在application/controllers/category.php 中的控制器

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
class Category extends MY_Secure {
function __construct()
{
    parent::__construct();
}
 public function index()
{
 $data['login'] = $this->session->userdata('login');
 $data['status'] = $this->session->userdata('status');
 $this->load->model('categories_model');
 $data['main_categories'] = $this->categories_model->get_main_categories();
 $this->load->view('admin/headers/main', $data);
 $this->load->view('admin/category');
 $this->load->view('admin/footer/main');
}
?>

但是我有一个错误Fatal error: Class 'MY_Secure' not found in Z:'home'ci.local'www'application'controllers'admin'category.php on line 3我该如何避免这个错误？我做错了什么？