Patent attributes
An automated purchase transaction analyzes a purchase transaction using a probability model to determine a probability that the transaction is fraudulent. If the probability exceeds a threshold, the transaction may be manually reviewed to determine whether to freeze the account associated with the transaction. When introducing the model, the threshold may be set to a relatively high value so that a small number of transactions are submitted for manual review. After a period of time, the observed freeze rate resulting from manual reviews is compared to a target freeze rate. The threshold is then adjusted upwardly or downwardly to decrease the difference between the observed and target freeze rates.