avast account screen indicates 3 devices; I only have one computer
my last update check from my machine indicates that last update received was 8/15 , indicates all shields on
but on the devices listed at the account website online; "My avast "
last communication 5 days ago - Firewall and DNS shields off
last communication 6 days ago - all shields on
last communication 1 week ago - all shields on
How are devices created ?
It is created when you link an installation to your my.avast.com account.
If you were to uninstall and reinstall it is possible that it would be considered a 2nd device.
You should be able to delete the devices from your my.avast.com account, that would remove the linkage in your current/only installation and you would have to link it to your my.avast.com account again.
What avast version (latest build 2015 10.3.2225) do you have installed free/pro/Internet Security/Premier ?