I got the message this morning and since my phone is rooted I'm glad it wasn't an automatic upgrade. I postponed it until I was able to find how to cancel the update. If anyone wants to prevent the update you have to uninstall (or freeze?) the apk file "Device management 3.0". I used Titanium backup to uninstall it, after making a backup of the file. Now when I choose "software update" in settings, it doesn't open the app, which shows me the uninstall is working and I won't be prompted to update in the future.