>You think banks aren't hacked?

There has been a lot of general description of the individual or group that performed the splitting as an "attacker" or "hacker", but the very nature of the system in question subverts the conceptual foundation of "attacking". To be an "attack" rather then a legitimate execution of an agreement, the action would have to be "illegitimate", but when legitimacy is explicitly defined by the code itself, then how can any action allowed by the code be illegitimate? It'd be a different issue entirely if the underlying VM or a system had been exploited, but merely doing as the code allowed when the code is made the agreement's authority?

Also, I've been using "agreement" here too rather then "contract" because, despite the label of "smart contract" Etherium has adopted I think there's a basic legal question about whether legally they're "contracts" at all. A contract is a subset of the space of agreements; all contracts are agreements, but not all agreements are necessarily contracts. There are many factors in determining validity of contracts and a huge body of contract law that has already been discussed a great deal, but all that depends on there being a contract at all, and for that there needs to be an agreement where the parties intend to be bound by the law (of whatever jurisdiction whose enforcement power they wish to invoke). There are many agreements where there is no intention to have legal enforceability, and in that case the courts have nothing whatsoever to say on the matter. Contract law never even enters the picture.

The DAO, and Etherium in general, have made a big deal specifically about not invoking the courts. That was supposed to be part of the entire point of smart "contracts", that they'd have nothing at all to do with any common legal system and be self-contained in and of themselves. In turn though that could mean that any smart contract that declares itself fully self-definitional is in turn not a contract period, so there cannot be an "attacker" in the legal sense.

Bank hacks in contrast aren't much different in concept from bank heists of any other kind. They are able to invoke real world power in response, and have multiple levels of fallbacks and insurance for their customers. It's by design a much softer fail, multiple level system with an expectation of occasional failure built-in and a strong human element. This adds expense and inefficiency, but provides benefits to imperfect human societies too. It came out of ages of real world experience and testing after all.