The percentage of servers receiving automatic patches is the best key control indicator (KCI) to monitor the effectiveness of patch management, because it measures how well the patch management process is ensuring that the servers are updated with the latest security patches and fixes. A high percentage of servers receiving automatic patches indicates that the patch management process is effective and efficient, and that the servers are protected from known vulnerabilities and threats. The other options are not the best KCIs, because they do not directly measure the effectiveness of patch management. The percentage of legacy servers out of support, the number of unpatched vulnerabilities, and the number of intrusion attempts are examples of risk indicators or consequence indicators that measure the exposure or impact of the lack of patch management, but not the performance or outcome of the patch management process. References = ISACA Certified in Risk and Information Systems Control (CRISC) Certification Exam Question and Answers