@julian Thanks, I'm aware of suggested topics, we're already using that but it gets topics from other categories too. Which doesn't work when you just want to focus on certain type of topics (a category) only.
@julian Using the registration queue would add a lot more work for admins/mods though - but certainly it would help with this also.
Looks like the above has helped, but we are still getting some registrations - the spam accounts are now just putting the URL in the "Full name" field.