Nearly 40% of PCs have not transitioned to Windows 11, leaving about 500 million users vulnerable after the official retirement of Windows 10 on October 14. The deadline for users to secure their systems coincides with Microsoft's first security update for Windows 10 PCs not enrolled in the Extended Security Updates (ESU) program, which offers a 12-month extension for essential patches. Many users may not be enrolled in ESU, increasing their risk of cyberattacks. In Europe, some PCs may not support the Windows 10 ESU, making Windows 11 the only viable upgrade option. Users attempting to enroll in ESU updates may face temporary unavailability in their region, and a workaround requires a potentially challenging in-place upgrade to Windows 10. Microsoft warns that outdated operating systems are prime targets for cybercriminals, and upgrading to Windows 11 is crucial for those eligible.