Here again, any WMDs (mostly Bio/Chem types)that Terrorists may get hold of are also heavily accounted for, other than those that Saddam smuggled into Syria before the war started. Those are not easy to move out of the immediate region however, because of the difficulty of transporting such devices.
In addition to that, most Bio/Chem devices have a short useful life and are more dangerous to any one stupid enough to try to conceal one. They would most likely wind up being the only casualty.