Valve commented on leaked source code
Valve reported that the source code leaked the day before Counter-Strike: Global Offensive is an old version that does not pose a threat to players. The current version of the game has fixed all the vulnerabilities.
We have reviewed the leaked code and believe it to be a reposting of a limited CS:GO engine code depot released to partners in late 2017, and originally leaked in 2018. From this review, we have not found any reason for players to be alarmed or avoid the current builds.— CS:GO (@CSGO) April 22, 2020
However, Tyler McVicker, from whose environment the leak occurred, said that he was not personally involved in the incident. The known insider has identified the culprit and will send the evidence to Valve.
On April 22, an archive with the source code CS:GO and Team Fortress 2 was published online. The leak caused concern in the community as the data could have been used to create new cheat programs or to access players' computers through official game servers.