Filter Driver

A filter driver attaches above or below another device package to inspect or alter input and output requests without replacing the main hardware controller. Antivirus tools, storage encryption, VPN clients, accessibility software, and device utilities can all install filters. Windows users may notice them only when a status code mentions an UpperFilters or LowerFilters problem, or when hardware works after the related application is removed. Because filters share the device stack, an outdated one can break a perfectly healthy base package. Update or uninstall the application that owns the filter first. Editing class-filter values in the Registry should be a documented last step, with the exact key exported beforehand, since removing the wrong entry can disable other devices in that class.