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Homeland Security

What Is Security and Resilience?


Presidential Policy Directive 21 (PPD-21): Critical Infrastructure Security and Resilience defines security as reducing the risk to critical infrastructure by physical means or defense cyber measures to intrusions, attacks, or the effects of natural or man-made disasters.

Examples of security measures: badge entry at doors, using antivirus software, fencing around buildings, locking computer screens.


PPD-21 defines resilience as the ability to prepare for and adapt to changing conditions, and withstand and recover rapidly from disruptions. Resilience includes the ability to withstand and recover from deliberate attacks, accidents, or naturally occurring threats or incidents.

Examples of resilience measures: developing a business continuity plan, having a generator for back-up power, using building materials that are more durable.

Last Published Date: May 8, 2015

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