App-specific password for iMessage on different Macs
For reasons that are not clear to me, my iMac at home did require a new password for iMessage. Before the reboot that I did after the Adobe & Microsoft updates iMessage did work, after the reboot it did not work but asked for an app-specific password. I could generate this app-specific password via my iCloud account, and with that submitted iMessage did work again.
Now to the questions:
1) Why does iMessage (I use only iMessage, not FaceTime) suddenly require this new password? There were plenty of reboots that I did earlier, and also many software updates.
2) Can/should/must I use the same app-specific password for iMessage on the different Macs (home, office, Laptop) I have? And on the iPhone as well? As far as I can tell, these iMessage instances all run currently with my "main" iCloud/AppleID password submitted for the iCloud account in (System) Settings.
iMac (21.5-inch, Late 2013), OS X Yosemite (10.10.3), Fusion Drive, 16 MB RAM