An apparatus and method are disclosed for determining authentication frequency (i.e., the length of time between authenticating and re-authenticating a user) and challenge type (e.g., username/password, fingerprint recognition, voice recognition, etc.) based on what software applications a user is running on a data-processing system, and how those applications are being used (e.g., what functions are used, what data is input to or output by the application, how often and for how long applications are used, what input devices and output devices are used, etc.) Advantageously, the illustrative embodiment enables authentication frequency and challenge type to be adjusted based on the likelihood of malicious activity and/or the potential cost of malicious activity, as inferred from current and past application usage. In addition, the illustrative embodiment enables selection of an authentication challenge type that is less intrusive to a user based on current application usage.