refers to the specialization of computer network security that consists of technologies, policies, and procedures that protect networked computer systems from unauthorized use or harm. Broadly speaking, cybersecurity topics can be subdivided into two complementary areas: cyber attacks, which are essentially offensive and emphasize network penetration techniques; and cyber defenses, which are essentially protective and emphasize counter-measures intended to eliminate or mitigate cyber attacks.

Cyber attack: An offensive action by a malicious actor that is intended to undermine the functions of networked computers and their related resources, including unauthorized access, unapproved changes, and malicious destruction. Examples of cyber attacks include Distributed Denial of Service (DDoS) and Man-in-the-Middle (MITM) attacks.

The increasing reliance of our information-age economies and governments on cyber (computer-based) infrastructure makes them progressively more vulnerable to cyber attacks on our computer systems, networks, and data. In their most disruptive form, cyber attacks target the enterprise, government, military, or other infrastructural assets of a nation or its citizens. Both the volume and sophistication of cyber threats (cyber warfare, cyber terrorism, cyber espionage and malicious hacking) are monotonically increasing, and pose potent threats to our enterprise, government, military, or other infrastructural assets. Knowing that to be forewarned is to be forearmed, we are well advised to effect strong Cybersecurity defenses that will thwart rapidly evolving cyber threats.
Recent newsworthy cyber attacks on critical cyber infrastructure (e.g., Target data breach, Mt. Gox bitcoin hacker attacks, NSA data leaks and subsequent PRISM revelations) demonstrate the urgent need for improved cybersecurity. As cyber threats grow, so must our abilities to neutralize them. Towards that end, the U.S. government issued an Executive Order for Improving Critical Infrastructure Cybersecurity in February 2013, and the 2014 President's Budget devoted over $13B to cyber-related programs and activities [Federal Information Technology FY 2014 Budget Priorities, p. 15]. The European Union Agency for Network and Information Security (ENISA) lists all known public documents of National Cyber Security Strategies in the EU, as well as the rest of the world.

cyber threat: A potential cyber attack, which may be assigned a probability of occurrence that can be used for cyber risk assessment.

cyber risk: A risk assessment that has been assigned to a cyber threat, such as DDoS attack or a data breach. A cyber risk assessment may be either qualitative or quantitative, where the latter should estimate risk (R) as a function of the magnitude of the potential loss (L) and the probability that L will occur (i.e., R = p * L).