Ubuntu keeps rebooting and displays message that safeboot dbx has been updated (opens in new tab)

My situation is different in that the system has been running perfectly (like a dream, actualy). While it is running and I am using it, all of a sudden, it shuts down and immediately starts to reboot. Sometimes it displays the motherboard introduction screen and I have to hit F2 and enter the BIOS utility, exit that and restart or sometime it immediately displays the Ubuntu login screen. On each occasion the message appears at the top of the screen that an important update to the OS has been ...