Social networking poses three primary threats to national security according to the speaker: [1] Open intelligence collection through social engineering and oversharing of personal information, [2] Back office data collection where personal details are aggregated and used for hyper-targeted advertising, and [3] Propaganda dissemination as social media allows information to spread quickly with little verification. The speaker argues that social networking is the greatest threat as it can enable cheap surveillance of individuals and attacks the "weakest link", which is humans oversharing personal details online. Mitigation involves educating users and monitoring for security lapses from employees.