I found something that should help people having problems with Offline mode or don't want to go online at all. I do not know how well this works to stop the update process.
http://pcgamingwiki.com/wiki/Steam#Always_Force_Offline_Mode
Always Force Offline Mode
Forcing Offline Mode will make Steam to always open in Offline Mode, even with a working internet connection. A prompt will appear and the options Retry and Offline Mode will show up. Retry will simply restart Steam and cause the same menu options to come up, whereas Offline Mode will take one into the Steam game library.
This step still requires the authentication to be carried out.
Create or edit the
in this folder (the same folder as the steam.exe):
Enter the following and save:
Code:
BootStrapperInhibitAll=enable