Examples relate to methods of printing a 3D printed tamper evident security structure for protecting a feature; the method comprising repeatedly: depositing a layer of build material; doping one or more than one region of the layer of build material using a dopant to influence a respective electrical attribute of one or more than one region associated with a graph of the structure; and agglomerating one or more than one selected portion of the layer of the build material, including the one or more than one doped region of the layer of build material, to form progressively the graph with a predetermined measurable electrical characteristic.