Updated from the Appstore, the computer rebooted with no issues (I was with OS X 10.10.1).
Then I ran Multibeast 7.4.1 to fix all the possible issues generated by the update, I've overwritten the audio driver too (ALC 892) and after that the Audio volume coming from the speakers started being very low compared to the volume before the update. Even setting the OS X volume to the max, the speaker volume to the max too, the audio was still not loud at all (I expected it should have blown me away).
I then ran an old version of Multibeast (7.1.1) overwriting the ALC892 driver again and everything went back to normal.