THE risk of an unsecured nuclear weapon falling into the hands of al-Qa'ida or other terrorist organisations posed the greatest threat to global security, US President Barack Obama warned yesterday. Mr Obama said he knew al-Qa'ida was trying to obtain a nuclear weapon and would have no compunction about using one to cause devastation. The President issued his warning before today's start of a two-day summit of 47 countries that he is hosting in Washington. The Nuclear Security Summit, the first of its kind, is meant to focus on ways to secure supplies of plutonium and highly enriched uranium that...