This rule detects unauthorized modifications made to the Windows registry specifically to disable the BlockAtFirstSeen feature of Windows Defender. It focuses on monitoring registry changes within the Windows Defender SpyNet path, mainly looking at the 'DisableBlockAtFirstSeen' value. When this setting is altered to enable (with a value of 0x00000001), it indicates that the BlockAtFirstSeen feature is turned off, allowing potentially harmful files to evade detection by Windows Defender during their first encounter on the system. Such a modification raises severe security concerns as it may facilitate malware infiltration, enabling malicious actors to execute their code without triggering alerts from Windows Defender, thereby heightening the danger of system compromise and data breaches. The detection leverages data from Sysmon and analyzes registry operations to ensure immediate alerts can be raised for security teams to investigate promptly.