Which of the following best describes volatile data?

Volatile data refers to information that is temporarily stored in a system's memory and is lost when that system is powered off or rebooted. This type of data is critical in various scenarios, especially in forensic investigations and security assessments, as it may hold valuable information regarding active processes, open network connections, and other pertinent details that are only available during runtime.

In the context of the other options, permanent storage mediums like hard drives do not qualify as volatile since they retain data even when the power is off. Similarly, data that can be modified without risk does not capture the essence of volatility since all data has the potential to be altered; the key aspect of volatility lies in its temporary nature, not its modifiability. Lastly, data on removable devices does not inherently indicate volatility, as it can be either permanent or temporary depending on the usage and device type. Thus, the best description of volatile data centers on the fact that it is indeed at risk of loss during system reboots or power failures.