This joint booklet highlights 42 indicators—or observable behaviors—that suggest an ideologically motivated US-based violent extremist may be mobilizing to violence. This supplement is intended to show how these indicators can be used to help detect threats against 16 critical infrastructure sectors.

  
To report any leads, threats, or suspected criminal activity, you may  visit https://tips.fbi.gov/ or contact your local FBI field office: https://www.fbi.gov/contact-us.

 Note: Do NOT use this website to report emergencies or immediate threats to life. Call 911 for emergencies or immediate threats to life. 

In this report, the authors discuss threats to critical infrastructure (CI) and put forward a hypothetical case study to examine several phases of an adversarial attack on the United States. The attack is intended to constrain U.S. decisionmaking, disrupt military deployment, and impose strategically relevant costs on the civilian populace.

The authors aggregate CIs into seven classes to demonstrate how an attack on any one of these categories can have outsized effects because of interdependencies between infrastructure assets, systems, and networks.

Because of the interconnected nature of CI systems, damage to one system can adversely affect another. This may lead to a cascading hazard, producing disruptions across geographic boundaries and CIs.