Google indexing forum pages duplicate content

For some reason even though i have all the SEO modules installed that reduce duplicate content from all the other places, the forum topics still get indexed by google multiple times with the url "?sort=asc&order=Replies." It will index the same page multiple times by changing the order=replies to things like order=topic and what not. Is there a way to fix this? Or is it not even a problem? Is there something i can add to robots.txt?