That form of military science that, by the employment of devices and/or techniques, has as its objective the impairment of the operational effectiveness of undesirable or adversarial activity, or the prevention of espionage, sabotage, theft, or unauthorized access to or use of sensitive or classified information or information systems.

1. defensive countermeasures include actions to identify the source of hostile cyber activities' protection/mitigation at the boundary (e.g., intrusion protection systems (IPS), pre-emptive blocks, blacklisting); hunting within networks (actively searching for insiders and other adversaries or malware); passive and active intelligence (including law enforcement) employed to detect cyber threats; and/or actions to temporarily isolate a system engaged in hostile cyber activities.
2. offensive countermeasures might include electronic jamming or other negation measures intended to disrupt an adversary's cyber capabilities during employment.