Message about Apple ID used in another Mac I have received this message in the screen:

"Your Apple ID is now being used for iMessage and FaceTime on a new Mac."

I indeed updated OS in another Mac, which would be an explanation for this message, according to previously solved questions on this matter. 

... but I updated it three days ago, and that machine is supposed to be switched off, far away from here.
Should I worry?
Does the expression "is now being used" mean that it is being used at this precise moment?
The message you got is to notify you that you have singed in on the mac you updated with your apple ID.

Normally you should receive this message on other devices that are connected with your apple ID.

That you received the massage after 3 days could have something to do with the recent outage of some apple services, but I'm not sure about this