This extension is installed by the Mac OS 8.5 installer and should not be removed, even if other modem software is installed. Removing this extension prevents you from making Ethernet connections.
If you have experienced other difficulties since installing Mac OS 8.5 please read the About Mac OS 8.5 Read Me and Installing Mac OS 8.5 Read Me that come with Mac OS 8.5.
This information is from Article 58129: "
Mac OS 8.5: About Mac 0S 8.5 Read Me".