[Minnie]

I think what you are describing is or was called Tachy Goes To Coventry - or Global Ignore. I believe there's also something called Troll Hack. With Troll Hack they would see periods of slowness, non responsiveness, 404 pages, posts won't go through, etc. The site sort of works, sometimes, but mostly it's like they're stuck in a loop of just not quite staying online long enough to actually do anything. It's been a while since I saw the inside of a vB admin panel though so who knows what subsequent upgrades have kept or dumped.

ETA: anyone can have a look at the inside of a vBulletin admin panel at any time. vBulletin allows for trial accounts where you can sign up for 72 hours to have a poke around their system to see if you want to use vBulletin or not. You can see anything usable for troll control, member features, etc.