elseif ($_REQUEST['act'] == 'signin'){
    if (!empty($_SESSION['captcha_word']) && (intval($_CFG['captcha']) & CAPTCHA_ADMIN)){
        include_once(ROOT_PATH . 'includes/cls_captcha.php');
        /* 检查验证码是否正确 */
        $validator = new captcha();
        if (!empty($_POST['captcha']) && !$validator->check_word($_POST['captcha']))
        {//此处有严重逻辑错误，也就是说我不post验证码就可以不检查验证码了
            sys_msg($_LANG['captcha_error'], 1);
        }
    }
    $_POST['username'] = isset($_POST['username']) ? trim($_POST['username']) : '';
    $_POST['password'] = isset($_POST['password']) ? trim($_POST['password']) : '';