That reminded me, it was about time to do a purge of non-posting accounts and those that haven't visited for yonks. We're now back to a smaller but more elite membership (with some notable exceptions of course, on both counts).
We have indeed been getting fairly frequent visits from the spammers, both human and robotic. I've rubbed all the paint off my delete key. Today I've applied some mods to help trap them at the front door; to help me spot any that slip through; and to allow me to report them to t'internet cops. Thanks for the prompt Nick.
Asking more rigorous questions on registration had occured to me as an option when first setting the forum up. I haven't gone (and don't currently intend to go) down this route as I'd prefer to keep it open to everyone, regardless of whether they understand what we're on about or not.
Excluding people who don't know what we're on about would probably rule out 99.999999999999% of the word's population.