NEO uses the dBFT consensus mechanism to achieve “Byzantine Fault Tolerance” between nodes in consensus system. The NEO Whitepaper says that if the number of malicious bookkeeping nodes is less than 1/3, the dBFT consensus mechanism can guarantee the security and availability of the system. However, our research found that the NEO’s current implementation of dBFT mechanism only guarantees a consensus between honest bookkeeping nodes.

http://blogs.360.cn/post/NEO_dBFT_en.html