A new paper by Ittay Eyal and Emin Gun Sirer claims that Bitcoin mining is vulnerable to attack. They say the attack is not nearly as scary as they indicate. The paper argues that an ES-miners build a secret chain of blocks which they hope will grow longer than the ordinary block chain. The result of the ES attack is that a block made by an ESminer is less likely to be orphaned than by an ordinary miner, but it turns out that one made one by an orphaneds attack turns out to be a result.”]
Source: https://freedom-to-tinker.com/2013/11/07/bitcoin-isnt-so-broken-after-all/