There's an easy way to eliminate spam posted by spambots.

Create a new usergroup for user with 0 posts and don't allow this group to create their own threads until they've reached a certain post number. This number is up to the admin to decide but 1-5 should be good. And once they reach this post number they will be bumped to another user group with default settings.

Hope you get what I mean.

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It’s not made by hundreds of people, hundreds of computers,
hundreds of things that can’t be touched, seen or
understood.
The Zonda F is made by hand, by Maurizio, Pirta, Tiziana,
Gnacca, Fazio and just a few others; by people who put
their heart and soul into their work