Advanced nuclear weapons designs may have been sold on black market

Which groups or nations may have bought electronic blueprints for an advanced nuclear weapon? That’s the question for American and international investigators who say the plans for a small nuke were found on the computer network of rogue Pakistani nuclear scientist Abdul Qadeer Khan, who has been under house arrest for the past four years. The Takeaway talks with New York Times reporter David Sanger, who has been following this story for a year.