Steam – check what version is Steam gift

If you want to do this without starting Steam and logging in, you can modify the setting in the Windows registry. The autostart checkbox is directly tied to a registry key — simply deleting it is all the Steam client does when said checkbox is unchecked.

Navigate to HKCU\Software\Microsoft\Windows\CurrentVersion\Run and delete the Steam key. Or as a .reg file:

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run]
"Steam"=-

I know this is an old question, but...

Steam re-validates games that you own approximately once a month.

This is one of the steps Steam uses for fraud prevention, as Valve will pull games from accounts purchased using fraudulent sources.

You may say "Wouldn't Valve just ban the account?" They likely ban the purchasing account. However, Steam users can gift games to other accounts or trade them through Steam trading... the recipient can't tell if the originator got the item in a fraudulent manner.

This is largely transparent to users... unless you're offline for more than a month.