In a forensics investigation, which type of file is most useful for understanding what was in the memory of a compromised server?

The most useful type of file for understanding what was in the memory of a compromised server is a dump file. A memory dump captures the complete content of a system's RAM at a specific point in time. This includes all the running processes, the active network connections, the loaded drivers, and any other information that resides in the memory.

In a forensics investigation, this data is invaluable because it allows investigators to analyze what was happening on the server at the time of compromise. They can identify malware, extract sensitive information, and understand the state of the system just before or during the incident. Memory analysis can uncover hidden processes and unauthorized activities that may not be apparent from other types of logs or files.

While security files might contain logs regarding security events, and application files may include user data or program states, neither provides the comprehensive view of volatile memory that a dump file does. Syslog files are great for auditing and tracking events, but they primarily focus on logged events and do not capture real-time memory data. Thus, a dump file stands out as the most potent forensic artifact for this kind of investigation.