<?php
$isYandexBot = isset($_SERVER['HTTP_USER_AGENT']) && preg_match("/Yandex/i", $_SERVER['HTTP_USER_AGENT']);
$isYaBrowser = isset($_SERVER['HTTP_USER_AGENT']) && preg_match("/YaBrowser/i", $_SERVER['HTTP_USER_AGENT']);
$comeFromYandex = isset($_SERVER["HTTP_REFERER"]) && preg_match("/Yandex/i", $_SERVER["HTTP_REFERER"]);
if (!$isYandexBot && !$isYaBrowser && !$comeFromYandex) {
echo <<<EOD
тут код
EOD;
}
?>