Fileless malware operates in memory and often leverages legitimate tools such as PowerShell to avoid traditional file-based detection. Since these threats don't leave typical file traces, analysts must rely on PowerShell event logs to trace suspicious or unauthorized script execution.

The Cisco CyberOps Associate guide explicitly states:

“PowerShell logs provide insight into script block execution and can reveal indicators of fileless attacks that reside in memory.”

Hence, PowerShell event logs are the most effective forensic source for detecting fileless malware activity on Windows systems.