1. A method of detecting attempted fraud at a self-service terminal, the method comprising: providing a classifier having a plurality of input zones, each input zone being adapted to receive data of a different modality; mapping inputs from a plurality of sensors in the self-service terminal to respective input zones of the classifier; for each input zone, independently operating on inputs within that zone to create a weighted set; combining the weighted sets using a dedicated weighting function for each weighted set to produce a composite set; and deriving a plurality of class values from the composite set to create a classification result.