A ransomware incident is a type of cyberattack that encrypts the victim's data and demands a ransom for its decryption. Ransomware can cause significant disruption and damage to critical systems and data, as well as financial losses and reputational harm. To recover from a ransomware incident, the organization needs to have reliable and accessible backups of its data, preferably in an encrypted format. However, if the backups are unavailable or corrupt, the organization will face a major challenge in restoring its data and operations. Therefore, option D is the most challenging factor for the recovery of critical systems and data following a ransomware incident. References = CISA MS-ISAC Ransomware Guide1, page 9; How to Write an Incident Response Plan for Ransomware Recovery2.