If any "request" to your forums on classic, it will log it in the wol asif they even logged in; if yoru boards are closed to non members then there is no real worry.
As for not allowing the invisible setting, you could just edit it out of the template file then you woudlnt have to worry about anyone selecting it.
An example, if i go to your forums, and it says i cna't access it, it'll still log me attempting to view your forums, thus i would display on the classic who's online bar.
