A method and system for identifying patterns of payment account (e.g., credit card account) transactions that have a high probability of being part of a fraudulent scheme. Certain merchant accounts and payment accounts may have been obtained under false pretenses. For example, the payment accounts may have been obtained with the intention of never paying the bills with a true instrument. Merchant accounts may have been obtained in order to perform transactions either with payment accounts obtained under false pretenses or with stolen payment account information. To detect suspicious patterns of account activity, payment accounts that are new or exhibit a substantial increase in account activity are first identified. Merchant accounts having an unusually large number or value of transactions with such new or newly active payment accounts are also identified. Such merchants and payment accounts can then be subjected to further scrutiny by the affected institutions.