Nowadays, most important topic about internet banking is security. Banks? basic concern is ensuring their customers? electronic transactions. Nevertheless, fraudsters are becoming more sophisticated and they act really clever to achieve their target. Having this knowledge, banks try to optimize their detection systems in order to detect fraud and investigate suspect online behavior and transactions. Object of this paper is to demonstrate one successful fraud detection model which is established in Greece. Apart from the offline internet banking fraud detection system itself, which is described briefly, our scope is to present its contribution in fast and reliable detection of any "strange" transaction including fraudulent ones.