EtherDelta

EtherDelta is an exchange with hybrid centralized and decentralized features. Most operations are handled directly on the blockchain. A trader never needs to let go of the the ownership of their tokens, enabling the system to deal with transfers and trades in a trustless manner.

The weak point of EtherDelta's architecture is the centralized order book server. In case a bad actor took control of the orders, they would be able to trade against those orders or delete them. Deletion of orders would remove all liquidity from the exchange and render it unusable.