VX is a nurve agents that stays present after awile, instead of evaporating completely. Just like a other agent used in WW 1 ( mosterd ? ). VX is avaible in large quantaty's by various country's. Weather terrorist has them or not, nobody really knows ( exsept for terrorists, ofcorse... )

i'm by no mean a expert, this is just what i have read.... ( unless mine brains are letting me down again )