Today, with development of technologies and communication networks, cyber security is one of the challenges in widespread use of cyber-physical systems. Secondary control in microgrids is known as one of the potential targets of cyber-attacks, and these threats should be considered in the design of the controller. In this paper, the vulnerability of distributed secondary control against cyber-attacks has been proposed. This paper studies the performance and vulnerability of various distributed secondary control methods in AC microgrids under cyber-attacks. The purpose of this work is to identify the point of failure of each method against cyber threats in AC microgrids. In order to do this comparison study, three well-known attacks including false data injection, controller hijacking, and denial of service are evaluated for three secondary control methods so called distributed consensus, average distributed control, and distributed finite-time control. Simulation results are performed in MATLAB software to provide the comparison results.