User blog comment:-Merca/Hardmode Here I Come!/@comment-72.177.214.102-20120311210401/@comment-4674838-20120311211433

You can just put Wood (or some other non-corruptible material) on the ground across the surface. And then nothing can be corrupted. Alternatively, you can "quarantine" the corruption by building a huge Wood box around the corruption biome, that way any corruptors that spawn don't get out of the box and can't corrupt your world.