Monitoring of a control should occur at a rate concurrent with the volatility of the security control when implementing Information Security Continuous Monitoring (ISCM) solutions. ISCM is a process that involves maintaining the ongoing awareness of the security status, events, and activities of a system or network, by collecting, analyzing, and reporting the security data and information, using various methods and tools. ISCM can provide several benefits, such as:

Improving the security and risk management of the system or network by identifying and addressing the security weaknesses and gaps

Enhancing the security and decision making of the system or network by providing the evidence and information for the security analysis, evaluation, and reporting

Increasing the security and improvement of the system or network by providing the feedback and input for the security response, remediation, and optimization

Facilitating the compliance and alignment of the system or network with the internal or external requirements and standards

A security control is a measure or mechanism that is implemented to protect the system or network from the security threats or risks, by preventing, detecting, or correcting the security incidents or impacts. A security control can have various types, such as administrative, technical, or physical, and various attributes, such as preventive, detective, or corrective. A security control can also have different levels of volatility, which is the degree or frequency of change or variation of the security control, due to various factors, such as the security requirements, the threat landscape, or the system or network environment.

Monitoring of a control should occur at a rate concurrent with the volatility of the security control when implementing ISCM solutions, because it can ensure that the ISCM solutions can capture and reflect the current and accurate state and performance of the security control, and can identify and report any issues or risks that might affect the security control. Monitoring of a control at a rate concurrent with the volatility of the security control can also help to optimize the ISCM resources and efforts, by allocating them according to the priority and urgency of the security control.

The other options are not the correct frequencies for monitoring of a control when implementing ISCM solutions, but rather incorrect or unrealistic frequencies that might cause problems or inefficiencies for the ISCM solutions. Continuously without exception for all security controls is an incorrect frequency for monitoring of a control when implementing ISCM solutions, because it is not feasible or necessary to monitor all security controls at the same and constant rate, regardless of their volatility or importance. Continuously monitoring all security controls without exception might cause the ISCM solutions to consume excessive or wasteful resources and efforts, and might overwhelm or overload the ISCM solutions with too much or irrelevant data and information. Before and after each change of the control is an incorrect frequency for monitoring of a control when implementing ISCM solutions, because it is not sufficient or timely to monitor the security control only when there is a change of the security control, and not during the normal operation of the security control. Monitoring the security control only before and after each change might cause the ISCM solutions to miss or ignore the security status, events, and activities that occur between the changes of the security control, and might delay or hinder the ISCM solutions from detecting and responding to the security issues or incidents that affect the security control. Only during system implementation and decommissioning is an incorrect frequency for monitoring of a control when implementing ISCM solutions, because it is not appropriate or effective to monitor the security control only during the initial or final stages of the system or network lifecycle, and not during the operational or maintenance stages of the system or network lifecycle. Monitoring the security control only during system implementation and decommissioning might cause the ISCM solutions to neglect or overlook the security status, events, and activities that occur during the regular or ongoing operation of the system or network, and might prevent or limit the ISCM solutions from improving and optimizing the security control.