Drones and lone wolf attacks are key concerns as FBI works to secure 11 World Cup cities

By Holmes Lybrand, CNN HUNTSVILLE, AL (CNN) — On Thursday, the first whistle blew, ushering in the largest sporting event the US has ever hosted — or secured. Millions of foreign fans are expected to descend across the country for the World Cup, with the US hosting 78 matches across 11 cities and countless more