Techniques to detect unauthorized access and/or use of a user's account provided by an online web service are provided. A user's activity on the online web service can be monitored to determine a model of the user flow through the online web service. The model of user flow can be unique to the user or can be a model assigned to a cluster of users having similar behaviors or mannerisms when navigating the online web service. The model can vary based on the type of device used by the user to access the online web service. Once a model is determined, subsequent activity on the online web service by the user can be monitored and compared to the model of user flow. Unauthorized access and/or use of the user's online account can be detected if the subsequent activity fails to fit the model of the user flow.