China announced a ban on initial coin offerings on Monday- which caused cryptocurrencies to stumble briefly. This ban could go beyond ICOs- based on the language of the ban- which may include cryptocurrency exchanges. But that isn"t the only blow to cryptocurrency this week. Nobel prize-winning economist- Robert Shiller said bitcoin is the best example of a bubble in the market today. Shiller is known for calling the last two bubbles before they happened and as the author of "Irrational Exuberance."