What tool should an incident responder use to monitor user and network activities?

The correct choice is a tool that is specifically designed for monitoring changes and ensuring the integrity of systems, which makes it highly relevant for incident response activities. Tripwire is particularly effective in detecting unauthorized changes to files, configurations, and system settings, which can be crucial during an incident investigation. By monitoring file integrity, it helps incident responders identify and respond to potential security breaches, as any abnormal alterations might indicate malicious activity.

In contrast, the other tools serve different functions that may not be as directly aligned with real-time monitoring of user and network activities. OSSIM provides a broader range of security information and event management (SIEM) capabilities, while Splunk Light, although capable of analyzing machine data and logs, focuses primarily on data analytics rather than direct monitoring for incidents. MBSA (Microsoft Baseline Security Analyzer) is aimed at assessing security configurations and vulnerabilities rather than continuous monitoring of user activity. Therefore, Tripwire stands out as the most suitable tool for the specific task of monitoring user and network activities within the context of incident handling.