Two things here:
First, it wasn't a virus embedded in an addon. Addons themselves are nothing but text (and occasional graphics) files. It was a trojan hidden in an executable that would self-delete the carrying executable as soon as it ran, to make it harder to trace.
Second, you're fine with Ace, this was at incgamers (formerly ui.wow.net).
You should be fine.
(Always better to check if you are unsure though.
)