Check out this too.
http://www.reddit.com/r/Bitcoin/comments/282z7a/im_selfish_mining_at_ghashio/Hello, I control somewhere between 50 TH/s and 2 PH/s(can't be too specific for security reasons) of hashing power. Today, I have been pointing some of this at Ghash.IO, and selfish mining to hinder their profits. I withhold blocks I find, and do not send them. I encourage others to do the same(towards Ghash.IO), to destroy this pool that is deliberately trying to harm Bitcoin.
Thanks.