US Patent 11748757 Network security systems and methods for detecting fraud

A system for detecting fraud within a payment card network includes a memory storing historical transaction data and a processor configured to identify a set of historical transaction data, the set of historical transaction data include one or more test transactions labeled as having been used to test validity of an underlying account, train a model using the identified set of historical transaction data as labeled training data, the model is configured to accept transaction data associated with an input transaction and to classify the input transaction as a test transaction, apply a suspect transaction of a cardholder account as the input transaction to the model, the model generates an indication that the suspect transaction is a test transaction, mark the cardholder account as compromised based on having experienced test transaction activity, and reject a pending transaction based on the cardholder account being marked as compromised.