Devices, systems, and methods of detecting user identity, differentiating between users of a computerized service, and detecting a possible attacker. The methods include monitoring of user-side input-unit interactions, in general and in response to an interference introduced to user-interface elements. The monitored interactions are used for detecting an attacker that utilizes a remote access channel; for detecting a malicious automatic script, as well as malicious code injection; to identify a particular hardware assembly; to perform user segmentation or user characterization; to enable a visual login process with implicit two-factor authentication; to enable stochastic cryptography; and to detect that multiple users are utilizing the same subscription account.