The notion of security as a general scientific category is defined as a condition of the system, in which she the one hand, able to withstand the destabilizing effect of internal and external threats, but with the other – its existence and operation does not create threats for the elements of the system and the external environment. In this case, the natural measure of security systems are presented: – in terms of ability to resist destabilizing impact of external and internal threats – the degree (level) to maintain a system of its structure, technology and performance of exposed destabilizing factors – in terms of absence of threats to elements of the system and external environment – the degree (level) the possibility (or impossibility) of occurrence of such destabilizing factors, which may present a threat to the elements of the system itself or external environment. ; Purely mechanical interpretation of the above formulation leads to the following definition of information security. ; Definition 1.1. Information security – a condition considered system, under which it is on the one hand, able to withstand the destabilizing impact of external and internal information threats, and with another – its existence and operation of information does not create threats to elements of the system and the external environment. It should be noted that information as an indispensable component of any organized system, on the one hand, is vulnerable (that is very accessible to the destabilizing effects of large number of diverse threats), and the other may itself be a source of too big and too diverse number of threats for both elements of the system itself, and for the environment.