1. A method of classifying detection inputs as belonging to a first class or a second class depending on a numerical score associated with each input comprising the steps of: scoring a multiplicity of detection inputs to produce a set of scores; comparing each of the scores with a first threshold, if at least one score exceeds the first threshold, classifying in the first class all inputs having a score that exceeds a second threshold lower than the first threshold, and if no score exceeds the first threshold, classifying none of the inputs in the first class.