Adding this here, since I found it to be extremely relevant.
From an unnamed third-party contractor who was contacted to help resolve PianoWorld/Frank's issue:
After many questions:
He [Frank/PianoWorld] finally fessed up that somebody had attempted to move 15,000 members to another group. because they have a default group that is temporary then they manually move then to the normal user group after a few posts.
And that is when the problem came up.
I mentioned the [automatic] post count option [built in to stock UBB.threads] but that is the way they want it.
--
A side-observation not really related to PianoWorld/Frank's issue, but its a feature which should be used:
Also from that third-party contractor:
The logs have never been purged so it takes forever to go over them.
Linking this here, to help anyone else who may stumble across this thread:
From the UBB.threads 7.6.2 Changelog -
[NEW] Admin Logs can be automatically purged to a certain age (Lifetime). The auto-purge feature is disabled by default. (CP > Primary > Logging)
https://www.ubbcentral.com/forums/ubbthreads.php/topics/261663/7-6-2-changelog-discussion
