What security measures are required to counter the potential availability of weapons of mass destruction to transnational terrorists?

Effective security measures aimed at preventing the acquisition, manufacturing or usage of the weapons of mass destruction (WMDs) by terrorist groups, should include the protection of key materials, required to fabricate a WMD, from being acquired by terrorists (particularly important, in this respect, is the prevention of nuclear smuggling); increasing cooperation between regional and national police forces and intelligence agencies; and improving the effectiveness of the counterterrorism intelligence agencies by eliminating rivalries between them (especially between those within the same country) while mandating them to share information and cooperate with each other (Barnaby, 2004). 

References

Barnaby, F. (2004). How to build a nuclear bomb: and other weapons of mass destruction. New York: Nation Books.