Interconnected

I approve (as if they needed it). BountyQuest is anti bad patent, pro good patent. They're a clearing house for corporations to offer money in bounty to people who can find prior art to patents, such as Amazon's 1-click and even the BountyQuest business method. The company vision and history is also interesting reading.

Question: After a patent is granted and then prior art is found, how from there is a patent invalidated?