A merger with another organization would likely require a revision to the information security program because it can result in significant changes to the structure, size, and information systems of the merged entity. This can affect the security requirements, risk tolerance, and governance policies of the organization. To ensure that the information security program remains effective, it is important to review and revise the security policies, standards, and procedures in light of the changes brought on by the merger. The information security program should align with the new organization's risk tolerance, security requirements, and governance policies. This information can be found in the ISACA's Certified Information Security Manager (CISM) Study Manual, Section 3.1.

Updating the plan periodically has the greatest positive impact on the ability to execute a disaster recovery plan (DRP). This is because an up-to-date plan is more likely to reflect the current environment, and any potential risks or issues can be addressed before an emergency arises. Storing the plan at an offsite location, communicating the plan to all stakeholders, and conducting a walk-through of the plan are all important steps, but they do not have the same impact as regularly updating the DRP.