Sign in/out

I will often sign in to Messenger on my office PC only to get a message at
some time during the day saying that I have been logged out as I have signed
in at a different location.

My home PC is on but I have not signed in to Messenger on it.

This is really annoying as messages are directed to the home PC instead of
the one at which I am working in the office!

Can anyone please explain why this happens, and how I can prevent it?

Thanks.

DG


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