An update with an early build of Left 4 Dead was unexpectedly released for CS

Valve studio unexpectedly released another update for its shooter Counter-Strike, which even more unexpectedly added a new mode to the project.

It is based on the concept of an early version of another shooter called Left 4 Dead. Initially, the game was called Terror Strike, and it was an activity in which terra survivors needed to shoot back from counter-terr zombies and try to plant a bomb in a building.

The developers promptly deleted the Left 4 Dead files from CS, but vigilant players still managed to copy them and send them to the public.