Over the past few days we've had an absolute flood of registrations, all with similar, long, nonsensical names. Most real human beings prefer a username which makes sense, which got my suspicions up. When I did some research, it became clear that there were in fact dozens of automated registrations going on, by so-called 'SPAMbots'. The anti-SPAM system here is pretty good, but those pesky bots had obviously managed to find a way around it -- and scanning the web it appears as though it's a problem affecting many forums out there.
I've banned a series of email addresses (the ones most commonly used by spammers) and installed a new, improved anti-SPAM system today which seems to have staunched the flow quite satisfactorily. I guess it's only a matter of time before the SPAMmers find a new way to beat the system, but until then, peace reigns