This week, outdated source code for Valve’s Team Fortress 2 and Counter-Strike: Global Offensive was posted in the public domain, causing concern it could be used to circumvent security in these games.
The code – dumped on 4chan – was old and outdated, and Valve was soon able to issue a pair of statements saying it had detected no threat to either of its games. But where had this source code come from, and why was it being spread online now?
According to Valve, this code was not only several years old, it had also been leaked before.
Source: Eurogamer TF2, CS:GO source code posted by disgruntled modder booted off Portal fan project