Just the Bestiary section.
I got the warning pop up when I did the EXP Mob Search, a feature I wish another website had it or even Campsitaru.
Anyway, after searching for monsters to EXP off of, you will get a list of monsters per usual in the search results. Clicking any of the monsters brings up that Avast warning window.
Therefore, it's anything and all tied to a single PHP file that displays the monsters stats, if you try to open it up.
For example, let's say you click on a monster in the search results and the URL is:
Vana'diel Bestiary - Stray
Code:
http://monsters.ffxi-atlas.com/monsters/?id=2156
... if I click it, Avast throws up a warning about finding "HTML: script-inf" virus on that particular page.
EDIT: DON'T CLICK THAT URL. IT'S ONLY MEANT TO BE AN EXAMPLE.
EDIT #2: It seems BG Forums auto-formats the Bestiary URL and concatenates it into what the URL links to. You may want to change that...