In global mobile network, it is required to authenticate mobile users, provide secure communication channel between a user and a foreign agent using session key and guarantee users’ anonymity and untraceability. In order to improve the security of mobile roaming service, two-factor authentication which employs smart card and pass-word was introduced to global mobile network. In 2014, the researcher proposed an anonymous two-factor authentication scheme for mobile roaming service. However, the authors found that this scheme is vulnerable to four kinds of man-in-the-middle attacks and denial-of-service attack.