During the UK riots, the British government asked Blackberry to block messages sent between protesters. Recently in San Fransciso, Bay Area Rapid Transit officials shut down cell service to curb a planned protest. Zeynep Tufekci, assistant professor of sociology at the University of North Carolina-Chapel Hill and author of the popular blog technosociology.org, discusses whether blocking social media is a legitimate law enforcement tool in a time of social unrest.