Final answer:
Compensating controls provide a partial solution when a primary security control cannot completely meet a requirement due to practical limitations. They address risks in alternative ways and maintain security at an acceptable level.
Step-by-step explanation:
The best description of compensating controls is: a partial control solution that is implemented when a control cannot fully meet a requirement. This usually happens in situations where it is not feasible or too costly to implement the ideal control, possibly due to technical limitations or other constraints. Instead, compensating controls are put in place to address the risk in a different way, albeit less directly or with less efficacy than the primary control would. They should still meet the intent of the original security requirement and reduce risk to an acceptable level.
For example, if an organization is unable to implement multi-factor authentication on a system due to compatibility issues, it might enforce strong password policies and regular password changes, monitor account access patterns, and use anomaly detection as compensating controls. These controls act as an alternative or backup measure to minimize the risk posed by the failure or inadequacy of a primary control. For example, if a firewall fails to block all unauthorized network traffic, an Intrusion Detection System (IDS) can be implemented to detect and alert the security team of potential security events.