Methods and apparatus are disclosed for authenticating a user based on the geo-location history of a geo-location-enabled wireless device (e.g., a GPS-enabled wireless telecommunications terminal, a smart card, an RFID tag, etc.). In a first illustrative embodiment, a user of a geo-location-enabled wireless telecommunications terminal (e.g., a GPS-enabled cell phone, a GPS-enabled notebook computer, etc.) who attempts to access a restricted resource is challenged with one or more questions that are generated from the terminal's geo-location history. In a second illustrative embodiment, a user of a data-processing system who attempts to access a restricted resource is asked to provide a username Z. The user is then challenged with one or more questions that are generated from the geo-location history of a wireless device that is associated with username Z (e.g., a cell phone that belongs to the user whose username is Z, etc.).