Latest investigations on the MtGox case suggest that hackers found a possibility to create new accounts with a fake (fiat) balance. They used this to buy Bitcoin and withdraw them. This buys could have been the main reason for the price raise last November. We have just written a blog post on it with more details: http://blog.fairlay.com/2014/08/connecting-the-dots-a-possible-connection-between-the-raise-in-november-mtgox-disaster-and-recent-price-drop/