The UN has warned that the increasing incidence of smuggling and illegal trade in chloroflourocarbons(CFCs) could seriously undermine efforts of over a decade to eliminate the consumption and production of the ozone depleting substance.The UN warning comes on the enve of World Ozone Day on September 16.CFCs are the largest threat to the earth's ozone layer and are the most dangerous of the entire range of the ozone depleting substances that have been identified for elimination by the Montreal Protocol.