Microsoft Confirms April Updates Cause Backup Failures
Microsoft has confirmed that its April 2026 security updates are triggering backup failures by blocking the psmounterex.sys driver used by third-party software.
Microsoft has officially confirmed that the security updates released in April 2026 are causing backup failures for users relying on specific third-party applications. The issue stems from a conflict with the `psmounterex.sys` driver, which is being blocked by the updated security configurations [BleepingComputer].
The problem primarily impacts enterprise and consumer environments that utilize third-party backup solutions dependent on this driver. Users experiencing these failures may find that their backup processes are interrupted or unable to complete, potentially leaving systems without recent recovery points until the conflict is resolved.
Microsoft is currently investigating the issue and has advised users to check for updates from their backup software vendors, who may need to release patches to ensure compatibility with the new driver block policies. In the meantime, administrators may need to evaluate their backup configurations or temporarily adjust security settings if the backup functionality is mission-critical.