Before revision:  We first show that black-box MT systems can be stolen by querying them with monolingual sentences and training models to imitate their outputs.
After revision:  One setting of particular interest is machine translation (MT), where models have high commercial value and errors can be costly. We investigate possible exploitations of black-box MT systems and explore a preliminary defense against such threats. We first show that black-box MT systems can be stolen by querying them with monolingual sentences and training models to imitate their outputs.