Systems, methods, and software can be used to share content. In some aspect, an electronic device selects a base station to camp on. A first message is sent from the electronic device to the base station. The first message is addressed to a server and requests the server to send a second message to the electronic device. Whether the electronic device receives the second message from the base station within a threshold time period after the first message is sent is determined. The electronic device determines that the base station has a security risk based at least in part on whether the second message is received within the threshold time period.