Valve has decided to increase the security level of Steamworks. The company notified the developers that now they will need to link a phone number to the account.

Steam will send an SMS with a confirmation code to it when the developer wants to add new users to the account or update the build of the game / application. Valve noted that the code will not be needed only for beta versions and projects that have not yet been released.

Also, if a developer releases builds via the SetAppBuildLive API, then now he will need to specify a specific SteamID linked to the mobile application for confirmation.

The change will take effect on October 24, 2023. In the future, Valve plans to expand SMS verification to other actions in Steamworks.

Valve did this shortly after hackers broke into the accounts of several small developers and infected the demo versions of their games with malware.

A source:

Steam Community