[Simon Lloyd]

The ones that get through will be human!, they cant "inject in to the database" as that would imply a huge security flaw.

I agree it is annoying but you'll not stop paid human spammers. There are some scripts that read q&a and keep trying known words like "What colour is the sky?" they'll recognise that phrase and the script will roll through colours, you'd have to make the q&a more complicated and require email confirmation too, that will cut many of your spammers, then use something like "bad behaviour" or "stop forum spam".

Lastly have new registrations go in to moderation and access to only one welcome forum for posting, now you've narrowed it down to one forum which makes it easier to clean-up anad you or staff can vet each and every new member - hey presto no spam!

It all boils down to how much trouble you want to go to in order to stop them.