The most effective way to limit the impact of a ransomware attack is to have data backups. Data backups are copies of the data that are stored in a separate location or device, and can be used to restore the data in case of a loss or corruption. Data backups can help to recover the data that is encrypted or deleted by the ransomware, and to avoid paying the ransom to the attackers. Data backups also help to reduce the downtime and disruption caused by the ransomware attack, and to maintain the business continuity and availability of the data. Cyber insurance, cryptocurrency reserve, and end user training are not the most effective ways to limit the impact of a ransomware attack, as they may not prevent or recover the data loss, and may incur additional costs or risks for the enterprise. References = Risk and Information Systems Control Study Manual, 7th Edition, Chapter 5, Section 5.1.1.1, page 2281

1: ISACA Certified in Risk and Information Systems Control (CRISC®) Exam Guide, Answer to Question 657.