Microsoft's latest security update for Windows 11, released in April 2026, has introduced significant issues for users of third-party backup software. This update, identified as KB5083769, impacts Windows 11 versions 24H2 and 25H2 and has led to a level 3 advisory from security expert Susan Bradley at AskWoody. The problem stems from a malfunction in the Volume Shadow Copy Service, a crucial Windows component used in creating snapshot-based backups. This malfunction causes backup jobs to fail, either stalling or timing out, which poses a risk to data integrity for both individual users and businesses. While several vendors have acknowledged the issue, it's important to note that not all backup solutions are affected. Microsoft's own cloud-based Backup feature in Windows 11 remains unaffected since it does not depend on the Volume Shadow Copy Service. Additionally, Microsoft's upcoming Point-in-Time Restore feature, still in preview, does not add further risk to standard users. For those experiencing issues post-update, it's advised to check with your backup solution's vendor for specific impact details. Administrators are advised to delay the deployment of this update in production environments until Microsoft releases a fix, which is expected in an upcoming out-of-band update or the May 2026 cumulative update.