Recently, Valve made a tweet on the official Team Fortress 2 twiiter basically coming out to say the current builds of TF2 and CS:GO are fine. TF2 and other source games should all be perfectly safe to play now! Thank you all for your participation and cooperation in trying to keep our community safe. This group will be removed in a little bit.

Good news is that we have official confirmation that CS:GO is not affected by the source code leak. They tweeted out that the leak was from a repost of a limited CS:GO engine code depot given to their partners in late 2017 and released to the public in 2018. Garry's Mod may also now be safe to play. I received information that it uses an entirely different version of SDK2013. While this is great, we are still unsure of other source games at the moment. As for Team Fortress 2, the game is currently unsafe to play, and is beginning to fill with hackers who are capable of stealing peoples' accounts and their items.