By the way, I don't believe that the attacker shorted a lot of Ether.

In order to short sell an asset, you have to loan the asset from someone, immediately sell it, and then after the price crashes, buy it back and return to the creditor. If there is any difference, you pocket it. If the asset raises in price, you now have to pay more in order to buy the asset back, and you can run into a large loans.

However, the problem is that it is not trivial to get this much Ether loaned to you if you don't have a lot of capital to begin with. Ether is a new and unstable asset, there are a very few places that can loan you Ether in the first place. And those who do won't loan you a lot of it, unless you provide a good collateral, and even then, you can only get a limited amount, because there is simply not a lot of short-sell offers out there.

And if he did short it, he wouldn't have stopped at 31%, but would continue siphoning all the way so that the Ether price would crash even more.

In short, I don't believe attacker made a lot of money with this. Although I respect the discovery and execution of his attack, I don't feel bad about the fact that he didn't make any money with it, because it was still an attempted theft.

To those who are saying that this attack was trivial. Not exactly.

First of all, the attacker did not just use previously published recursive call vulnerability, he discovered a couple more exploits on top of that. It was a well done work that included multiple steps. Then, it took at least 4 days for all the researchers to understand how exactly the attack was made.

If you have seen the chat rooms, you'd know that well-respected Ethereum experts spent quite some time reproducing the attack. As additional proof to the difficulty of the attack, notice how at least a week has passed after the initial siphoning before somebody else tried to siphon more funds. If the attack was simply a manner of creating one line contract, we'd have had new attacks within a day. And what's interesting, the last black hat siphoning attempt was a failure - the attacker did not create a good enough exploit which allowed white hat attackers to drain most of the funds very quickly.

That said, 50 people is of course a wild underestimation. It can be anyone, can be someone who had nothing to do with the Ethereum before deciding to poke around in the contract.