This research project supports “Usable Computer Security”, meaning design and evaluation of computer security technology from the perspective of human-computer interaction, ensuring that the security mechanism are easy and effective to use. A new approach to address this problem is “implicit authentication”, whereby the device itself monitors usage patterns to detect anomalous usage. When such usage is detected, re-authentication is instantly required. This safeguards access and credentials, and therefore also reduces incentives for theft. Our research will explore this area, beginning with exploration of user needs and preferences that will inform design and evaluation studies of novel approaches to implicit authentication.