This paper examines principles and approaches for proactive computer-system forensics. Proactive computer-system forensics is the design, construction and configuring of systems to make them most amenable to digital forensics analyses in the future. The primary goals of proactive computer-system forensics are system structuring and augmentation for automated data discovery, lead formation, and efficient data preservation. This paper proposes: (1) using the Neyman-Pearson Lemma to proactively build online forensics tests with the best possible critical regions for hypothesis testing, and (2) using classical stopping rules for sequential hypothesis testing to determine which users are deviating from standard usage behavior and should be the focus of more investigative resources. Here the focus is on security breaches by the employees or stakeholders of an organization. The main measurements are event-driven logs of program executions.