Looking for a PLUGIN to stop in appropriate registration on blog and forum

How do I stop people that are registering that seem not legitimate such .ru and viagra registerants. I thought of approve user register but everyone seems to have unusual email addresses. I was thinking of having a rule that in order to register you need to make one quality post but now it is set that need to register to post.

If someone registers and doesn’t post can they still do stuff malicious on your blog and forum if you don’t see any postings by them.

So, I would like a plugin that says in order to register for the site you need to make one post either in comments or forum that is user approved.

Any help would be greatly appreciated