A hacker accessed a University of Florida dental school server containing personal information for over 344,000 current and former patients. An investigation found unauthorized software installed on the server from an outside location. Meanwhile, Express Scripts, one of the largest US pharmacy benefit firms, received an extortion letter threatening to disclose personal and medical data of millions of Americans if a payment demand was not met. This module discusses how computer data breaches occur through various methods, and how to investigate local machines, networks, and implement countermeasures to prevent future breaches.