AppleBluetoothBroadcom64 is not properly signed
The bootcamp ( 6.1.7438 ) driver for Apple made bluetooth cards is not properly signed and therefore cannot be used unless booted with disabled signature checks. It seems to be signed with some development certificate:
Without deactivating the checks this is what you see when you try to install the driver:
After disabling the checks by using advanced startup options the install is possible. You see a warning but it will install and operate the device flawlessly:
The device in question: VID = 05AC (Apple) PID = 828F
I guess Apple just needs to not forget to properly sign the driver when they update the Bootcamp software. I have no idea what might be the best way to contact the about that. The Feedback Bug reporter does have no category that fits.
iMac Line (2012 and Later)