Which type of analysis requires the evaluation of a system or software while it is actively running?

Dynamic analysis involves evaluating a system or software while it is actively running. This method allows security analysts to observe the behavior of the software in real-time, providing insights into how it interacts with the system's resources, its performance under various conditions, and any potential vulnerabilities that may emerge during execution. By monitoring the software as it operates, analysts can capture information such as memory usage, system calls, and interactions with other processes, which are crucial for identifying runtime issues that may not be apparent in a static environment.

The other options focus on different aspects or methods of analysis. Static analysis, for instance, examines the code or structure of the software without executing it, making it impossible to observe dynamic behavior. Side-channel analysis targets information leakage through indirect channels during execution but does not inherently emphasize the evaluation of the software itself. Reverse engineering involves dissecting software to understand its components and design, which may or may not occur while the software is running. Thus, dynamic analysis stands out as the approach that directly involves active execution to collect meaningful behavioral data.