"Nuclear proliferation, especially to or by terrorist groups, is commonly regarded as one of the greatest, if not the greatest, threats we and other governments face. Yet the enormous difficulties confronting terrorists who wish to acquire, maintain, and then deploy a nuclear weapon or device suggest that the more likely threat is one posed by a state that either uses such a weapon or makes it available either to other governments or to a terrorist group. This point also applies to the procurement of possible biological weapons by terrorist groups where again dependency on the state plays a large role in obtaining the necessary materials. And if we are to judge from the analogy of the greatly hyped discourse on biological weapons proliferation and the wildly over-inflated assessments of the likelihood of biological warfare and especially such warfare perpetrated by terrorists using advanced bioweapons, the likelihood of terrorists acquiring and using nuclear weapons by themselves may also be comparably overstated, especially in view of the difficulties involved in obtaining, storing, preparing, and using both kinds of weapons. Therefore at present it seems like the most likely route of proliferation is by states to states or by agencies connected with a state to another state. Indeed, recent examples of proliferation like North Korea's construction of a reactor for Syria that was clearly intended for military purposes is an example of the phenomenon by which one state opens the way to another to become a nuclear power. Likewise, Syria and North Korea in this and other cases have used their own state-run illicit programs to fund these programs or to acquire the materials necessary to sustain them. Similarly Syria and Iran's transfer of weapons to Hezbollah exemplifies the pathway by which a state might enable terrorists to obtain desired military capabilities, be they conventional or nuclear."
Naval Postgraduate School (U.S.). Center for Contemporary Conflict: http://www.nps.edu/Academics/Centers/CCC/
Strategic Insights (January 2009), v.8 no.1