May 10, 2026, 6:28 am | Read time: 2 minutes
The April 2026 security update is once again causing issues for Windows. This time, data backup programs are affected. Microsoft has confirmed that the update may lead to failures in third-party backup solutions. Users notice the problems mainly when backups no longer function as usual.
Why Backup Programs No Longer Work Properly
According to a report by the online magazine “BleepingComputer,” the issue primarily affects applications that work with the Volume Shadow Copy Service. These include Macrium Reflect, Acronis Cyber Protect Cloud, UrBackup Server, and NinjaOne Backup. The disruptions occur on both Windows 11 and Windows 10, as well as Windows Server.
The background is a tightened security measure. Microsoft has added the driver “psmounterex.sys” to an internal list of unsafe kernel drivers and blocked it.
Microsoft Releases Urgent Update for Windows 11
Researcher Cracks Microsoft’s Recall Feature and Warns of Data Leak
Response to Known Security Vulnerability
With this measure, Microsoft is responding to a security vulnerability identified as CVE-2023-43896. Through this weakness, attackers could gain elevated privileges on a system or execute malicious code. Blocking the driver is intended to prevent this, but it also impacts existing backup solutions.
In practice, the error is particularly evident when using backup images. While backups can often still be created, mounting or restoring them fails. Users then receive corresponding error messages. This can be especially problematic when data needs to be quickly restored in an emergency.
Also of interest: Only a few days left! Popular Outlook app is disappearing
Microsoft Recommends Update Instead of Uninstallation
Microsoft advises against removing or pausing the April update. Instead, users and administrators should update their backup software to the latest version. New versions rely on updated and secure drivers that are not affected by the block. This can resolve the issues in many cases.