A question has still opened, should be the forum with some hundred or a thousand spam topic described, there is a possibility to delete this quickly (maybe as a plugin if I have overlooked), because I have found no way directly. Or are all messages deleted when I delete the user, as in Buddypress.
Best regards
Our Admin Bar plugin is handy for dealing with spam.
Yes, if delete a user, you will be asked if you want to delete their forum posts or reassign to another user.
I would also recommend our captcha plugin that stops the vast majority of automated spam posts – if not all of them!