Embodiments of the invention enable cardholders conducting an online transaction to be authenticated in real-time using a challenge-response application. The challenge-response application can be administered by an issuer or by a third party on-behalf-of an issuer. A challenge question can be presented to the cardholder, and the cardholder's response can be verified. The challenge question presented can be selected based on an analysis of the risk of the transaction and potentially other factors. A variety of dynamic challenge questions can be used without the need for the cardholder to enroll into the program. Additionally, there are many flexible implementation options of the challenge-response application that can be adjusted based on factors such as the location of the merchant or the location of the consumer.