South Korea offers a timely illustration of the relationship between social media and national security. Following the country's democratization in the 1990s and the explosion of communication technology since the millennium, citizens have joined the discussion of national interests and ideological conflicts, involving anti-Americanism, reunification and North Korea's provocations. South Korean media have influenced an ideological divide that distinguishes between young and old, haves and have-nots, security and nationalism, and pro and anti-North Korean sentiments. The author describes the trade-offs between security and civil liberties and how narratives advanced through social media differ from those reported by traditional news outlets.