One of the biggest hurdles in fighting terrorism is assessing the risk, U.S. Homeland Security Secretary Michael Chertoff said Thursday, as Muslim leaders debated extremism, and weapons experts warned of terrorists building a nuclear bomb. Each day countries are faced with a myriad of risks — to railroads, public transport and chemical plants — but officials need to look at the consequences, the vulnerability and the nature of the threats to prevent attacks, Chertoff said at the World Economic Forum in Davos, Switzerland. Full Story