Together with the development of new information technologies it is necessary to take actions the aim of which is to provide protection of ICT (information and communications technology) systems. Cyber security is mainly ensured by suitable systems with the installed software for counteracting cyber attacks, as well as by cyberspace-related legal regulations.In order to check the condition of cyber security, an analysis of ICT protection has been made in selected countries. The assessment of cyber security has been based on the analysis of work principles of military services, which, because of the type of the information possessed, are very rarely eager to show their potential in the area of information protection. The safety of stored and processed military data is currently an essential element because of the constant growth of reported cases of attacks on these data. Activities aiming at cyber space protection are undertaken also in Poland, and this is reflected in plans and programmes being created, as well as in the policy of protection of ICT critical infrastructure resources. In Poland the Ministry of National Defence is also engaged in the process of protection against computer incidents. It means that computer systems able to respond to computer incidents and protect the ICT critical infrastructure are built. Providing cyber security also requires analysing the legal aspects which regulate the issues of taking retaliatory actions against the ICT network of the opponent. The description of the legal aspect has been made on the basis of the analysis of the act in states of emergency, as well as a state of natural disaster, which regulate the concept of an external threat and of cyberspace. The analysis of cyber security will make it possible to indicate factors which are necessary to fight the opponent by means of the Internet. Moreover, the results of the present condition of cyberspace security will be compared to the expected one, which will allow formulation of conclusions to be applied for the effective detection and elimination of computer incidents.