The API for "Stop Forum Spam" is simple to install and use. That and a decent Captcha will stop 99% of spam.

Thanks for the suggestion, this is more than we'd usually see and the forum does have some captcha / bot detection but clearly it failed yesterday evening. I'll see what we can do to improve that.

I have seen & used the Stop Forum Spam site before so if there's an API to implement that, it should help.