Modem no longer works after startup/reboot in Mac OS X 10.10 (Yosemite)

MultiTech's modems that use the Exar USB-to-serial chipset recommend using a kernel extension (KEXT, aka driver) for operation. As of Mac OS X 10.10 (Yosemite), Apple requires these drivers to be signed to be able to load the driver in the OS (OS X 10.9 and older didn't enforce signing of KEXTs). Some of MultiTech's drivers were not signed, so they will not load and thus the OS prevents the use of the modem.


Update to the latest signed version (1.0.4 as of this writing):

Before installing 1.0.4, remove the old driver by doing the following:
1) In the Finder's Go menu, select Go to Folder....
2) Enter /System/Library/Extensions and go to that folder.
3) In the /System/Library/Extensions folder, find MultiModemUSBXR.kext and select it (click once on it).
4) Move MultiModemUSBXR.kext to the trash (e.g. File-->Move to Trash). You will need to supply the admin username/password to move it to the trash.
5) Now you may install the new driver which will be found in /Library/Extensions (the new location Apple recommends for 3rd party drivers).

Models affected: