The rule named 'Hosts File Modified' is designed to detect unauthorized changes to the hosts file across multiple operating systems, including Windows, Linux (Ubuntu and RHEL), and macOS. The hosts file is crucial for mapping IP addresses to hostnames and serves as the first point of lookup before DNS resolution occurs. If adversaries modify this file, they can redirect network traffic to malicious sites or disrupt communications essential for security measures, such as multi-factor authentication (MFA). For example, a documented incident involved Russian threat actors altering the hosts file on a domain controller, redirecting Duo MFA calls to localhost, which effectively disabled authentication for active accounts. This rule leverages both file event logs and process creation events to identify potential malicious activity. Analysts are advised to thoroughly investigate the context of the changes, including examining associated processes, user accounts involved, and any related alerts to ensure proper incident response and remediation actions.