xtra2015 on "Searching solution for malware redirect link"

Hi,
Google's technical team has contacted me because it seems to have found a redirect from our website (www.transambiental.com) that leads to a page detected as malicious. More specifically:

http://1182.xg4ken.com/media/redir.php?prof=1019&camp=6814&affcode=cr58&k_inner_url_encoded=1&cid=55804700655%7C32161%7Ctransporte%20mercancias&mType=&networkType=search&kdv=c&url%5B%5D=http%3A%2F%2Fwww.transambiental.com%2Findex.php

Leading to http://orders.buyhemat.com consisting as malicious.

I can not find that link, I've scoured the entire site, DataBase and code.
I can not upload a backup, because there is much new content that would be lost.

How do I get to find this link and delete?

Thank you.