NULLED PHP Script Anti Flood DDOS

PHP Code:

<?php

if (!isset($_SESSION)) {
    session_start();
}
// anti flood protection
if($_SESSION['last_session_request'] > time() - 2){
    // users will be redirected to this page if it makes requests faster than 2 seconds
    header("location: www.google.com");
    exit;
}
$_SESSION['last_session_request'] = time();
?>