Users report that modems refuse to work after installing Windows 11 update KB5074109, released in January 2026. Microsoft says it is not a bug, but a desired change.
The update change log specifies the removal of four legacy modem drivers: agrsm64.sys for 64-bit systems, agrsm.sys for 32-bit systems, smserl64.sys for 64-bit systems, and smserial.sys for 32-bit systems. Devices relying on these components no longer function within the updated operating system.
The change affects most recent devices
On Microsoft's Q&A forum, user Imsai8080 noted that a newly purchased modem, marketed as Windows 11 compatible, failed after the update. Restoring previous system state resolved the issue for both new and older modems. While some modem makers may issue an updated driver, the situation is worse for aged devices. The latter will no longer receive updated drivers.
Microsoft attributes the driver removal to unresolved security vulnerabilities in the legacy components. Eliminating these drivers strengthens the operating system's overall security framework.
Affected users may temporarily uninstall KB5074109 and pause Windows Update to restore modem functionality.
The January Patch Tuesday updates have become a real trouble for Windows 11 users. Due to bugs, the patches make devices unbootable, Outlook crashes, and prevent some systems from shutdown.
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