Devices, systems, and methods of detecting user identity, differentiating between users of a computerized service, and detecting a cyber-attacker. A user utilizes a desktop computer, a laptop computer, a smartphone, a tablet, or other electronic device, to interact with a banking website or application, a retailer website or application, or other computerized service. Input-unit interactions are monitored, logged, and analyzed. Based on several types of analysis of the input-unit interactions, a score is generated to reflect fraud-relatedness or attack-relatedness of the input-unit interactions. Based on the score, the system estimates or determines whether the user is an attacker, and initiates attack-mitigation operations or fraud-mitigation operations.