A web service provider identifies electronic devices that are associated with a particular user by using device parameters, and user agents strings to cluster the user's web service requests determine whether the requests in each cluster originated from a single device or multiple devices. For any cluster having requests from multiple devices, the provider will analyze the scheduling cookies associated with each request to determine how many devices submitted the requests in each cluster. The system will then store identified devices and their characteristics in a profile for the user. Then, when the user submits a new web service request, the web service provider can compare data in the request such as device parameters, user agent strings and/or cookies to identify the device from which the new request originated.