The present invention is directed to a method and system for automatically classifying an application into an application group which is previously classified in a knowledge base. More specifically, a runtime behavior of an application is captured as a series of events which are monitored and recorded during the execution of the application. The series of events are analyzed to find a proper application group which shares common runtime behavior patterns with the application. The knowledge base of application groups is previously constructed based on a large number of sample applications. The construction of the knowledge base is done in such a manner that each sample application can be classified into application groups based on a set of classification rules in the knowledge base. The set of classification rules are applied to a new application in order to classify the new application into one of the application groups.