Abstract
A computer implemented method of assessing the probability of fraudulent activity in an account to account payment is provided. The method comprises determining, based on previous credit balance settlement transactions between a first account and a card settlement account, that a first set of payment credentials is associated with the first account. It is determined that a second set of payment credentials are associated with the merchant account. A database comprising historical data indicating details of past payment transactions between the holder of the first set of payment credentials to the holder of the second set of payment credentials is accessed. A fraud probability engine is used to generate, based on the historical data, a fraud probability value for a transaction from a first account to a second account, wherein the fraud probability value is an estimate of the probability of the transaction being fraudulent.