After a bit more digging they seem have arrived at attempt/version 6 of their Ethereum scripting language: https://github.com/ethereum/cpp-ethereum/wiki/LLL-PoC-6#basi... Diving deeper and looking at their ToDo lists you find gems of security holes that are known to be difficult: https://github.com/ethereum/cpp-ethereum/wiki/TODO#soonish For instance, a simple network poisoning, notorious Sybil attack or trivial deliberate stack corruption in this case.

No known defense against Sybil attacks exists, which does not rely on either a central authority or full access to a social network graph.

Seems to me that proof-of-work blockchains basically are decentralized defenses against Sybil attacks.

The network part of the stack doesn't really need anything new, and I don't think Bitcoin has had any trouble with it.