In order to detect hacker attacks and take early countermeasures, this paper introduced a novel mobile botnet called CPbot which uses Google Cloud Messaging (GCM) to spread Trojan on Android devices. First, we presented the network model of this GCM based mobile botnet as well as its command and control (C&C) mechanism. Secondly, we illustrated the different roles that this botnet can play. Finally, we setup a simulation model to discuss the topology of this mobile botnet. The MATLAB simulation result shows that CPbot is robust against single point of failures and has good resiliency to shutdown attempts, its command dissemination is highly efficient and the bot App has very low battery consumption. This analysis indicates that mobile botnet is a leading threat to mobile network security; therefore we must deploy defense strategies against this botnet.