I didn't restart my computer immediately as I had more work to do online (dial up), so I expected Setup to complete next time I rebooted... but not every subsequent time!
Did you ask for more than one update, I mean, manually?
If not, you stay more than 4 hours connected... and receive a second update.
Anyway, if you do not want automatic updates, more than blocking it into the firewall, set up these options into avast settings
