The Commission believes that unless the world community acts decisively and with great urgency, it is more likely than not that a weapon of mass destruction will be used in a terrorist attack somewhere in the world by the end of 2013. The Commission further believes that terrorists are more likely to be able to obtain and use a biological weapon than a nuclear weapon. The Commission believes that the U.S. government needs to move more aggressively to limit the proliferation of biological weapons and reduce the prospect of a bioterror attack. Further compounding the nuclear threat is the proliferation of nuclear weapons capabilities to new states and the decision by several existing nuclear states to build up their arsenals. Such proliferation is a concern in its own right because it may increase the prospect of military crises that could lead to war and catastrophic use of these weapons.