With advances and technological innovations, a new domain for display of power emerged: the cyber space. Being a hybrid space where real and virtual features are molded to form it, the cyber environment provides facilities actors working in it and at the same time, vulnerabilities. States, therefore, note that domain as a way to supplement your skills and abilities, and even catalyze them.The purpose of this monograph is to analyze the rise, strengthening and impacts of cyber power at the State level as important phenomena to be discussed in the area of Homeland Security. The question that will guide this work is "Why China has decided to expand its cyber power in the first decade of this century?". The hypothesis to be verified and corroborated is that uncertainty and insecurity in the present international environment, together with the historical use of cyber power by the United States lead to a security dilemma, when the U.S. cyber power is perceived as a threat by China. Moreover, it will be ruled that the dilemma per se does not explain all the reasons, so this thesis also will show other players that generate cyber insecurity.