How to: Restrict registered users from having a home page link in profile
 

I know I have read about this somewhere and now cant find it.

I have set up a promotion that after a member makes 5 posts they are promoted from registered users -> Member

Now what I am looking to do is restrict the default group (registered users) from having a link to their homepage

but...

I still want the promoted group (Members) to be able to have a link to their homepage.

The ultimate goal is to give us time to catch spammers ect. and not allow them to link back to their site - except in post. It's a lot easier for us to moderate posts than user profiles - especially if the user never makes a post.