It looks as though a new version of SMF (the software which runs the Forum) has been released. Although I haven't upgraded to the new version, it would appear that this Forum has reverted to it's "as first installed" default settings and the changes I made have been undone. I'll have a look at this tomorrow, but at first glance, nothing has been damaged as such. I'll go through and re-install the mods I made when setting it up when I get 5 minutes.