- Identity theft is a crime in which hackers perpetrate fraudulent activity under stolen identities by using credentials, such as passwords and smartcards, unlawfully obtained from legitimate users or by using logged-on computers that are left unattended. User verification methods provide a security layer in addition to the username and password by continuously validating the identity of logged-on users based on their physiological and behavioral characteristics. We introduce a novel method that continuously verifies users according to characteristics of their interaction with the mouse. The contribution of this work is threefold: first, user verification is derived based on the classification results of each individual mouse action, in contrast to methods which aggregate mouse actions. Second, we propose a hierarchy of mouse actions from which the features are extracted. Third, we introduce new features to characterize the mouse activity which are used in conjunction with features proposed in previous work. The proposed algorithm outperforms current state-of-the-art methods by achieving higher verification accuracy while reducing the response time of the system.