From "top secret," like the names and locations of intelligence agents,  to "confidential," like the drinking habits of a prime minister, the federal government has a lot of sensitive information. What are the different levels of security clearance, and how does it all work?Helping us untangle this web is Juliette Kayyem, professor of international security at Harvard’s Kennedy School of Government, and national security analyst for CNN. She formerly served as Assistant Secretary for Intergovernmental Affairs at the Department of Homeland Security under President Obama.