You have been tasked with implementing a virus prevention plan on a group of Windows client computers. Which of the following should you carry out?

Implementing a virus prevention plan primarily revolves around ensuring that antivirus (AV) software is up-to-date and functioning effectively, as this software is specifically designed to detect, prevent, and remove malware, including viruses. By regularly updating the AV software, you benefit from the latest virus definitions and security patches, which enhance the software's capability to protect the system against newly released threats. This proactive approach is crucial to maintaining the security posture of the client computers.

File History is primarily a backup tool and does not provide security against viruses. Updating Microsoft Office, although important for security and functionality, is not directly related to virus prevention as it does not inherently protect systems from malware. Installing a rootkit scanner might be a useful practice in certain advanced scenarios but is generally not part of a standard virus prevention plan; it's more of a specific measure taken when one suspects a rootkit infection. Therefore, updating the AV software stands out as the most critical action to effectively implement a virus prevention strategy.