I've just added a new thing to prevent spam--one that will hopefully get rid of all these ridiculous forum posts! I'd hoped there was a way to make new forum posts moderated, but I haven't found one, and obviously adding a Captcha for forum posts hasn't worked. So I've created a new user type. Basically, this means that I have to manually give users the ability to post new threads in the forum; just signing up doesn't allow that. When I see a comment from a new user indicating that they are a real reader, not a spammer, I'll give that person permission to post forum threads, but it's not automatic.
So people who haven't gone through the sign-up process get their comments moderated; people who haven't commented yet don't get to create forum threads. Sorry to make this so complicated, but the spam gets out of hand otherwise.
The forum-thread spam wouldn't even bother me so much if it didn't get onto my Twitter feed. I would change the rules, or even turn off the auto-posting for the Twitter feed, but I can't seem to get into my account on the site that sends new things from this site to my Twitter. I've opened a support ticket with them but haven't had much help yet. It's just frustrating!
EDIT: I forgot to mention that of course I gave everybody who's commented before the new user role, so you can all start forum topics. If I missed anybody, do let me know! And if you have trouble commenting, or with any other aspect of the site, please feel free to email me (chatoyant.college at gmail dot com).