Anti-ddos from yandex

if (mb_stripos($_SERVER['HTTP_USER_AGENT'], 'yandex.com', 0, 'utf-8') !== false) {
$load = sys_getloadavg();
if ($load[0] > 2) {
header('HTTP/1.1 503 Service Temporarily Unavailable');
header('Status: 503 Service Temporarily Unavailable');
header('Retry-After: 3600');
die();
}
}