1. A method comprising: receiving, from a user device, a request to engage in a transaction using authentication information; ascertaining a unique device identifier for the user device; comparing the unique device identifier to a set of known device identifiers previously associated with the authentication information; and upon a determination that the unique device identifier is not included in the set of known device identifiers previously associated with the authentication information: analyzing a history of prior transactions associated with the authentication information; creating a list of selected transactions from the history of prior transactions by selecting only those transactions that fall within a specified time window, are associated with a device type of the user device and where made within a predetermined geographic distance of a geographic location of the user device when the request was received; and delivering a notification to a user associated with the authentication information wherein contact information and a format used for delivering the notification to the user is based on a previous contact information and a previous format used to deliver at least one transaction on the selected list of transactions.