Windows 10 PC compromised; wondering if I need to clean firmware or even junk the drives entirely

Understanding and Responding to a Potential System Breach on Windows 10: A Comprehensive Guide

Introduction

In today’s digital landscape, cybersecurity threats are increasingly sophisticated, making it crucial for users—whether casual or professional—to be vigilant about potential compromises. Recently, a Windows 10 user with a background in infrastructure and systems engineering reported a concerning security incident involving suspected malware execution, possible persistence mechanisms, and questions about extensive cleanup procedures. This article synthesizes their experience and provides guidance on how to assess, respond to, and mitigate similar threats.

Scenario Overview

The user discovered suspicious activity while working on their Windows 10 machine—specifically, an unusual command in the system’s run dialog that referenced PowerShell with a base64-encoded payload. Upon investigation, they identified:

• Evidence of malicious PowerShell commands executed on the system

• Use of memory-resident shellcode typical of malware loaders

• Detection of a Trojan identified as Trojan:Win32/Skeeyah.A!rfn by Windows Defender

• Scheduled tasks created for persistent execution

• Cached browser data containing potential indicators of compromise

• Concerns about potential firmware or drive-level infections

Assessment of the Threat

The key indicators of compromise (IoCs) pointed to sophisticated malware employing typical shellcode loading techniques:

• Memory-based payload execution: Allocate memory, write payload, change permissions, spawn threads—classic behaviors for stealth malware

• Persistence mechanisms: Scheduled tasks possibly re-triggering malicious scripts

• Network communication: Decoding base64 commands that connect to suspicious domains, indicating command-and-control (C2) channels

Despite antivirus scans and malware removal tools, the user remained concerned about undetected or embedded malware at lower firmware or hardware levels.

Recommended Response Steps

1. Immediate Mitigation

2. Isolate the System: Disconnect the affected machine from the network to prevent further data exfiltration or command execution.

3. Preserve Evidence: Create a complete forensic image or backup of relevant data and logs for analysis, if possible.

4. Conduct Full Malware Scans: Use reputable, updated antivirus and anti-malware tools like Windows Defender, Malwarebytes, and specialized tools for deep scanning.

5. Deep System Inspection

6. Review Scheduled Tasks and Startup Items: Remove any unfamiliar or suspicious entries.

7. Check PowerShell Logs: Enable and review detailed PowerShell logging (transcript, module logging, script block logging) for signs of malicious activity.

8. Inspect Browser Cache and Files: Look for abnormal or lingering