Iframe problem/virus not being detected by Norton

I have an iframe problem when I access FTP accounts.  Every time I change the homepage of one of my websites a iframe is added to the bottom of the code belonging to a site called goooogleadsence.biz.

 

I've ran a few checks on Norton and cannot find anything; but when I popped on to Firefox to see what this site was all about it had a big warning message - malware.  

 

Can someone/norton help me remove this malware; are Norton aware of it?