I left my laptop alone for about half an hour, and when I came back an update for Avast was available.
But to my surprise it is an update to the previous 12.3.2279 version ( see screenshots ).
Needles to say that updating results in that everything is already up to date.
What could have happened here ?
Greetz, Red.
It seems that I am not the only one.
My guess is, that this is a server-side problem that Avast has to solve.
For know I would advise you all to wait and do nothing, untill we know more.
If I am right a repair or reinstall won’t solve this.
Greetz, Red.
:o Signature failure!
See img
Greetz, Red.
The problem was indeed on Avast servers, and is fixed now 
Greetz, Red.
Not fixed on my computer.
How quick it will be fixed on your computer, most likely depends on the update time interval of your Avast.
Default is 240 minutes, but I have set it to 20 minutes, the minumum update time interval that works.
Or reboot your system.
Greetz, Red.
reboot of system got rid of the update message.
wonder what caused that in the first place.
It has been confirmed by an Avast Developer that the problem was on the update servers.
Greetz, Red.