Fraud detection and computer security have a number of interesting parallels as adversarial & technological ecosystems where systems have exploits and attack surfaces.With the advent of the on-demand economy, the window of time between purchase and service delivery -- the period during which businesses can typically aim to identify fraudulent activity -- is becoming shorter and shorter.I'll present a summary of the common ways which in which fraudsters attack online commerce - starting with traditional online storefront attacks, and moving on to the challenges faced in realtime marketplaces.I'll explain a number of the techniques and technologies employed in combating online fraud, and draw parallels with traditional network and application security practices.