Complying with regulations regarding notification is the most important reason for an organization to communicate to affected parties that a security incident has occurred, as it helps to avoid legal penalties, fines, or sanctions that may result from failing to notify the relevant authorities, customers, or other stakeholders in a timely and appropriate manner. Additionally, complying with regulations regarding notification may also help to preserve the trust and reputation of the organization, as well as to facilitate the investigation and resolution of the incident.
References = CISM Review Manual 2022, page 3151; CISM Exam Content Outline, Domain 4, Task 4.5