The 'Unusual Remote File Size' rule uses machine learning to detect abnormal file sizes shared by remote hosts, which may indicate lateral movement by attackers. This behavior typically involves adversaries aggregating data into larger file transfers to evade detection, focusing on exfiltrating valuable information from compromised systems. The rule analyzes data within a specified timeframe (the last 90 minutes) and triggers alerts at an anomaly threshold of 70. The rule operates within the Lateral Movement Detection framework and requires specific integration assets to be installed, including file events collected by the Elastic Defend integration. It includes detailed guidance on setup, potential investigation steps, and mitigative actions against detected anomalies, emphasizing the need for validating alerts to avoid false positives related to legitimate business operations.