With the wide application of information and communication technologies, a great number of cyber vulnerabilities threaten the security and stability of the power system. Therefore, this article analyzed the intrusion paths, the invasion mechanisms, and the possible consequences of most potential attacks in power communication networks (PCNs); a method for classifying and evaluating defense measures considering security indexes is also proposed. First, the typical structure and hierarchy of PCNs are sorted out. Second, we study the potential cyber attacks that may occur against PCNs and classify them into hot-spot attacks and nonhot-spot attacks based on academic research and statistical analysis of historical cyber attacks. Then, the potential target devices, propagation paths, and possible consequences to PCNs are analyzed in detail for different cyber attacks. Third, a security index system to assess the resistibility, recognizability, and recoverability of different defense measures is proposed. Based on the capability of different measures against cyber attacks, the defensive measures are classified into resistibility enhancement measures, recognizability enhancement measures, and recoverability enhancement measures. Accordingly, the mechanisms of different defense measures are analyzed. After that, the effectiveness of each defense measure is evaluated based on the degree of correlation between the defense measure and the security indexes.