A modeling language is used to analyze the complex and changing system of a major corporation targeted by an advanced persistent threat. The analysis reveals ways that the response to the attack could have been better addressed. This work serves both as an example for improving responses to sophisticated cyberattacks and a demonstration of how the use of a specific modeling language can aid in understanding large, complex, time-varying systems. The modeling language is designed to use the same language to discuss all aspects of such a system, whether technological, social, informational, organizational, policy, or something else. Further, the language intrinsically considers the time-varying nature of these aspects.