How to stop steam updating
If you're still having problems after trying all of the above, there are really only two options; A lot of falsehoods and general misinformation in this thread...
This window absolutely CAN be permanately disabled while starting up Steam, period, end of story.
Steam, by default, has the configuration where it automatically updates your game whenever it has a network connection.
Although this technique is very effective as Steam gets updated in the background while the user performs his tasks in the computer, it can also prove to be a nuisance for people who have metered/limited connections.
As you may have noticed, Steam tends to start up whenever you turn on your computer.
Since Steam cannot update unless it is open, this method also addresses the issue very efficiently.
This configuration will force Steam to only update your games on that specific time.
You leave all the Steam settings like they are and limit the bandwidth of Downloads.
This will ensure that Steam doesn’t consume speed greater than the one you specified and you will be able to perform other actions on the internet without any lag or delay.
Only update this game when I launch it: This option disables all the automatic updates of the game and forces the game to update only when you want to play it.
High Priority: Always auto-update this game before others: This option will automatically give your game priority as compared to others when updating.