1. A system for detecting user fraud in connection with automated teller machine transactions, comprising: means for measuring at least one biometric value for a user; means for comparing that value to a reference biometric value for that user; means for predicting the type of transaction to be requested by said user; means for comparing the predicted transaction with the transaction actually requested by said user; and means for determining whether the user is valid, based upon the biometric value comparison and the result of comparing the predicted transaction with the actual transaction if said biometric value comparison is not conclusive.