twitscroll.b virus

I have some questions about the HTML/twitscroll.b virus. My friend has a website that he created on his own (very basic) but now all a sudden when people visit his site it prompts you from your anti-virus that this HTML/twitscroll.b virus is in the file. So basically my first question would be, through what methods would someone be able to put this virus on his site? His site is using html/css/php/MySQL. I myself have never had any security issues with my websites and he hasn't given me his ftp information yet to look at his files to see the problem so for now I would like to see if anyone here can lend me some advice about this virus. Once I get his ftp information Ill post some snippets of code that anyone feels may be relevant to the problem if I don't see the issue myself right away. Thanks.

 

figured it out.