A method of categorizing a recent transaction as anomalous includes a) receiving information about a recent transaction and b) accessing information about one or more historical transactions. The one or more historical transactions have at least one party in common with the recent transaction. The method also includes c) determining a similarity value between the recent transaction and a transaction i of the one or more historical transactions and d) determining if the similarity value is greater than or equal to a predetermined threshold value. The method further includes e) if the similarity is greater than or equal to the predetermined threshold value, categorizing the recent transaction as not anomalous or f) if the similarity is less than the predetermined threshold value, determining if there are additional transactions. If there are additional transactions, incrementing counter i and repeating steps c) through f).