Forum registration help

7.X is closed... so thought I would ask in here although i'm using version 7.9.

Basically, I'm getting a huge amount of peope joining, I'm assuming its robots doing it... but they are leaving explicit content (only in their profiles, they don't post anything.)

Is there anyway to control this or stop it? I've had trouble upgrading to version 8 with this site, which I assume would be the best idea as I could just approve registrations...

Any other ideas?

Thanks in advance

Kate