I just had to remove the Virtual Pet Rock forum due to insane amounts of spam. It's been getting harder and harder to keep up with spam and phpBB is so widely used and well known that it's become almost impossible to protect against this. Mods that deal with spam are ineffectual, extremely cumbersome or require you to delve deep into code that really shouldn't be touched as you'll likely have to alter the code again and again every time an update or security fix arrives (and these arrive frequently as the code seems to be leaking like a sieve).
Yesterday I repaired some crashed tables again for the second time in as many days due to the fact that spammers flood the system and this morning I woke up to about 250 spam posts. As the admin interface of phpBB leaves a lot to be desired I had to remove these posts one by one and after about an hour I just gave up. I did install a mod and later a utility that claimed to be able to delete multiple posts but these were either non-functional or failed to do the job adequately, leaving many things to still be done by hand.
What nailed the decision for me was the fact I saw we had 1400 registered users and only about 35 of those were actual bona-fide members (we didn't require registration for the few months when the board was most active). There comes a point where you just have to give in and decide that the effort simply isn't worth it anymore.
In any case, the Virtual Pet Rock forums may be gone but here's the link from the last post I made just yesterday.
The Wheel - a short animation about two rocks.
Let this be a lesson that teaches us that all things human pass in the blink of an eye, in what geologists call Deep Time. Rejoice, for soon the spammers will be dust.