When you refer to advertising, are you talking about the links in their member pages? I already disabled the links in the "memberlist," but not on people's individual member pages. I figured that if they never post then nobody is going to see their username, click on it, and get to their member page and link their link anyhow.
I doubt that I will ever be able to stop automated systems from signing up fake membernames for spamming purposes, and I can't really checkout every person who signs up. I should see if there is a way to automatically delete members who haven't ever posted, but even that won't work perfectly.