Which agency is responsible for stopping attacks on U.S. and allied critical infrastructure at the source?

The Department of Defense, specifically through the United States Cyber Command (USCYBERCOM), is responsible for stopping attacks on U.S. and allied critical infrastructure at the source. This agency's primary mission includes defending the nation against cyber threats and ensuring the integrity of critical systems. USCYBERCOM focuses on offensive and defensive cyber operations, meaning it actively seeks to identify, prevent, and respond to cyber attacks before they can impact infrastructure or data.

This role is particularly crucial due to the interconnected nature of modern critical infrastructure, where threats can originate from various sources, including foreign entities and malicious actors. By taking action at the source, USCYBERCOM aims to not only mitigate current threats but also deter future attacks.

Other agencies, such as the FBI and the DOJ, primarily focus on law enforcement and legal prosecution of cyber crimes, rather than preemptive cyber defense. The Department of State may engage in diplomatic efforts related to cyber security but does not hold the operational command required to engage threats directly at their origin. Thus, the correct answer reflects the proactive stance taken by USCYBERCOM in addressing cyber threats to national security.