1. A computer-based method to block a robot data aggregator from accessing a website, the method comprising: analyzing business operations and session data associated with using a website, the session data being collected from a session history log of user sessions, including human user sessions and robot user sessions, that use the business operations while accessing and/or navigating the website; defining, based on the analyzing, a set of important features of the collected session data from the user sessions, a feature value for each feature in the set of important features being extractable from each user session; extracting a feature value for each feature in the set of important features from the session data collected from each user session; classifying the session data collected from each user session as being with a human user or a robot user; generating training user session data, the training user session data comprising: collected session data from each user session in the session history log; extracted feature values from the collected session data from each user session; and a classifier flag value indicating that the extracted feature values are from a user session with a human user or a robot user; training a user classifier builder with the training user session data to build a user classifier including a model of behaviors of important business operations using the website, the model being based on the training user session data and including a set of decision rules that the user classifier follows to determine a type of user of a user session as either a human user or a robot user, and to discriminate a user session with a human user from a user session with a robot user; and blocking access to the website by a robot user that has been determined, from user session data monitored from a user session, to have accessed and/or navigated business operations while using the website.