A method and data processing system are provided for determining if a machine learning model has been copied. The machine learning model has a plurality of nodes, the plurality of nodes is organized as a plurality of interconnected layers, and the plurality of interconnected layers includes an input layer and an output layer. The output layer has a predetermined number of output nodes for classifying input samples into a predetermined number of categories, where each output node corresponds to a category. An additional watermarking node is added to the output layer. The model is trained to classify the input data into the predetermined number of categories and into an additional category for the additional node. The additional node may be added to another model to determine if the another model is a copy or clone of the ML model.