php根据UserAgent判断返回服务器状态

前两天刷洞发现一木马样本，解密后打包出来！

<?php
//屏蔽搜索引擎
if(!empty($_SERVER['HTTP_USER_AGENT'])) {
     //各类浏览器UA
    $userAgents = array("Google", "Slurp", "MSNBot", "ia_archiver", "Yandex", "Rambler", "Baiduspider");
    if(preg_match('/' . implode('|', $userAgents) . '/i', $_SERVER['HTTP_USER_AGENT'])) {
        header('HTTP/1.0 404 Not Found');
        exit;
    }
}
?>