When I launched Steam and entered my login and password, I received a request for SG. I took a snapshot of the registry and files on the PC before entering the SG code. Then I activated my account and took a second snapshot. When comparing these images, I checked all the changes but did not find anything suspicious.
How does the system understand that I have activated the account and does not request SG again? After all, there must be some secret file or key on the PC which blocks this request.