The development of technology has changed the world economy and induced new political trends. The European Union (EU) and many non-EU member states apply the strategies of information society development that raise the level of information security (IS). The Serbian Government (Government) has adopted the Strategy for Information Society in Serbia by 2020 (Strategy), and pointed to the challenges for the development of a modern Serbian information society. This paper presents an overview of the open-ended questions about IS, critical infrastructures and protection of critical infrastructures. Based on publicly available data, some critical national infrastructures are listed. As a possible solution to the problem of IS, the Public Key Infrastructure (PKI)-based Information security integrated information system (ISIIS) is presented. The ISIIS provides modularity and interoperability of critical infrastructures both in Serbia and neighboring countries.