The refund period ended on Nov 30th 2011. If you recently purchased the game you will either have to go through the merchant you bought it from or Steam directly.
Steam has a one time only refund policy, so refunding this may use that up.
Another thing to keep in mind is that the Devs are saying the all clear should be around the end of the month, If you can't get a refund check back on the game then, you may find yourself surprised.