I assume that we are talking about security for the maemo devices? (like monitoring/closing ports, flash security flaws, managing certificates, etc...)
I certainly do not beleive that security by hiding works, especially when what is hidden can be found with google (my point is 99.9% of users won't look for security threads if they are not easy to find, 99.9% of hackers will find these threads even if they don't have their own subforum).
Nonetheless, visibility is not so important for the thread participants (it seems there are still few trades on the subject, and few participants), but to the end users of the maemo platforms, that really just need final advice.
As such, I am not sure a whole subforum is needed, but a sticky in the platform's subforum and/or acrued presence in the wiki certainly cannot harm.