Or should that be, Source source code? In any case, Valve seems to be unconcerned about the leaked code for both Team Fortress 2 and CS:GO, despite fears of exploits resulting in two community servers going offline temporarily.
Portions of the source code for both games, dating from around 2018, according to Steam Database, leaked online yesterday. It's not known who leaked the code or why, but concerns immediately followed that vulnerabilities for both games could soon be exploited, if not already.
According to Tyler McVicker of Valve News Network, Valve ignored repeated warnings that the leak had occurred back in 2018, stating that;
I was very aware of it, and in fact the warning signs of the original leak—it was very apparent, and then it did leak sometime in late 2018, and then my little group of Source Engine developers, all on this Lever Softworks Discord server, were discussing the leak and how to contain it, how to keep it from hitting critical mass. Because unfortunately if it had hit critical mass, it wouldn't really hurt any one individual in particular. It would hurt the Source engine development community as a whole, because if Source code leaks, Valve then pulls the ability to have that source code to develop off of.
It seems likely somebody else within the Source engine development community leaked the code, but their identity is currently a mystery.
According to the Team Fortress 2 subreddit, possible remote code execution exploits exist within the code, although this was never confirmed.
Valve has since addressed this worry, however, stating that they have not found any reason why "TF2 players [should] be alarmed or avoid the current builds". They went on to state they will continue to investigate the situation and update the community if they find anything to prove otherwise.
From our review, we have not found any reason for TF2 players to be alarmed or avoid the current builds (as always, playing on the official servers is recommended for greatest security).— Team Fortress 2 (@TeamFortress) April 23, 2020
Valve also released a similar message on the official CS:GO Twitter account, also stating there were no concerns and that players can continue to play the games as usual.
Still, this isn't a good image for Valve right now, and security is understandably at the forefront of many players' minds. Hopefully, any issues within the leaked code are quickly identified and patched, assuming they exist.