This terrifying but all-too-common scenario forms the basis for this white paper, which walks through a hypothetical exercise held following a major cybersecurity breach at a fictional organization. The exercise leverages the well-known MITRE ATT&CK framework — a globally accessible knowledge base of adversary tactics and techniques based on real-world observations — to understand the specific tactics used by the attackers, identifying vulnerabilities so that they can be quickly addressed to thwart future attacks.