Section: INFORMATION RISK MANAGEMENT

According to the CISM Review Manual, the information security manager's best course of action when security controls may no longer be adequate due to changes in the organization's environment is to perform a new risk assessment. A risk assessment is a process of identifying, analyzing, and evaluating the risks that affect the organization's information assets and business processes. A risk assessment should be performed periodically or whenever there are significant changes in the organization's environment, such as new threats, vulnerabilities, technologies, regulations, or business objectives. A risk assessment helps to determine the current level of risk exposure and the adequacy of existing security controls. A risk assessment also provides the basis for developing or updating the risk treatment plan, which defines the appropriate risk responses, such as implementing new or enhanced security controls, transferring the risk to a third party, accepting the risk, or avoiding the risk.
The other options are not the best course of action in this scenario. Reviewing the previous risk assessment and countermeasures may not reflect the current state of the organization's environment and may not identify new or emerging risks. Evaluating countermeasures to mitigate new risks may be premature without performing a new risk assessment to identify and prioritize the risks. Transferring the new risk to a third party may not be feasible or cost-effective without performing a new risk assessment to evaluate the risk level and the available risk transfer options.
References = CISM Review Manual, 16th Edition, Chapter 2, Section 1, pages 43-45.