One of the biggest concerns about 3d printing has been the ability to print out guns which can go undetected. This has all seemingly changed:

http://3dprint.com/1341/company-crea...-printed-guns/

The UK based company, Radio Physics Solutions has creted a hybrid radar/AI based scanner which can detected 3D printed guns from afar. Already several large organizations have expressed interest in the new scanning device, which include the US Department of Defense.