565217 phbb forum security

I need someone to boost our PHBB Forums' security. You need to apply the same solution to 5 of our forums. Currently, there are way too many spam accounts or unrelated users signed up to promote their own products. What we would prefer to see happening is after users sign up, an email is sent to the admin for user account approval. Or, if you have a better suggestion for dealing with PHBB forums' maintenance.