The site most certainly has been hacked, I get two alerts one on the favicon.ico file also a common tactic in hacking sites as this is loaded by the browser for the little icon in the address bar. There may not be a favicon.ico file and that would be what kicks off the custom 404 error page, so I would also check out any custom 404 error page if you have one as I believe this is also affected.
It isn't just that there is a link to fobana2009dc.com but an inserted script tag, see images.
The fobana2009dc.com site is blocked by firefox safe browsing as an attack site, so avast is correct in blocking the script tag in the first instance.