For the sake of argument, let’s assume they are lying. If they were to execute a 51% attack, they would cause the bitcoin network to fundamentally lose trust in the currency, leading to a tremendous drop in price. I estimate this would be far more crushing than something like the recent Mt. Gox fiasco. Although not impossible, it would be extremely challenging for bitcoin to recover. As one of the largest “shareholders” in the bitcoin economy, it would be highly irrational for Ghash.io (or any other large mining pool) to voluntarily tank the system. They would be doing themselves much more harm than good, sacrificing the entire system’s integrity and potential for huge, ongoing profits for a much smaller immediate gain. Government leaders do not always share the same disincentives to collapsing their own economies; despite destroying his country’s currency, Mugabe is still in power, and still a billionaire.