Registering a Co-installer
A co-installer can be registered for a single device or for all the devices in a particular setup class. A device-specific co-installer is registered dynamically through the INF file when one of its devices is installed. A class co-installer is registered manually or by a Custom Device Installation Application and an INF.
For more information, see
To update a co-installer, each new version of the DLL should have a new filename because the DLL is typically in use when the user clicks the Update Driver button on the device property page.