Today, October 14, 2025, marks a pivotal moment: Microsoft has officially ceased providing free security updates for most editions of the Windows 10 operating system. This is a critical transition that affects millions of users worldwide.

As a final bookend, Microsoft has released the KB5066791 cumulative update, which is the last free security package your Windows 10 PC will receive. Understanding this update and your resulting options is now essential to maintaining your security posture.

The Mandatory Final Update: KB5066791

The KB5066791 update is the culmination of Microsoft's October 2025 Patch Tuesday rollout for Windows 10. It is a mandatory update because it contains vital fixes for serious threats, including six zero-day vulnerabilities and 172 other security flaws.

  • How to Get It: The update should automatically install, but you can manually check by going to Settings Windows Update and clicking 'Check for Updates.'
  • System Impact: After installation, Windows 10 22H2 will be updated to build 19045.6456, and Windows 10 21H2 will reach build 19044.6456.
  • Significance: Once this patch is applied, your PC will be as secure as Windows 10 can be, but no further free security fixes will be provided from Windows Update.

The End of the Line: What the EOL Status Implies

The End of Support (EOS) means that beyond today, Microsoft will no longer offer:

  1. Free software updates from Windows Update.
  2. Technical assistance for the operating system.
  3. Security fixes for newly discovered vulnerabilities.

While your PC will continue to function normally, running an unsupported operating system exposes you to an increasing risk of cyberattacks over time, as any new flaws will go unpatched.

"After October 14, 2025, Microsoft will no longer provide free software updates from Windows Update, technical assistance, or security fixes for Windows 10."

Related: Windows 10 End of Support Announcement

Your Options for Continued Security

To keep your PC protected, you have two primary, supported pathways forward:

1. The Free Solution: Upgrade to Windows 11

Microsoft strongly recommends that all eligible devices upgrade to Windows 11. This is the only free solution for ongoing security updates and feature development.

  • Benefit: Long-term free security and access to modern features.
  • Consideration: Requires hardware compatibility (TPM 2.0, specific CPU generation). Crucially, ensure you have backed up your data before starting any major OS upgrade.

2. The Paid Solution: Extended Security Updates (ESU)

For users who cannot, or choose not to, upgrade to Windows 11, Microsoft offers a paid ESU program to bridge the security gap.

  • Enterprise/Commercial Users: Organizations can purchase up to three years of additional, paid security updates to manage large-scale migrations.
  • Consumers: You may enroll to receive an additional year of security updates, with specific regional programs (such as in the EMEA) potentially offering an initial year of ESU at no charge.

If your work or data demands that you remain on Windows 10, enrolling in the ESU program provides a necessary, though temporary, security lifeline.

The time to act is now. Whether through a full migration to Windows 11 or enrolling in the ESU program, taking steps today ensures your PC remains a secure and reliable platform for tomorrow.