C: drive

Selected users of Windows 11, particularly those with Samsung laptops, are experiencing an issue that makes their main C: drive inaccessible, displaying the error message "C: is not accessible – Access denied." This problem has been acknowledged by Microsoft and appears to have arisen after the February 2026 security update (KB5077181). It primarily affects users of Windows 11 versions 24H2 and 25H2 in regions such as Brazil, Portugal, Korea, and India. Microsoft is investigating the issue, which may be linked to the Samsung Share app, and has provided a potential workaround to roll back to a previous version via the Settings > Windows Update menu. Users have also suggested changing the ownership of the C: drive as a workaround, though this comes with risks.