Valve accidentally leaks Left 4 Dead prototype in Counter-Strike patch

The terrorist with the bomb must make it to the house and plant the bomb.

Zombies will respawn a little bit after being killed.

Once the bomb is planted, every zombie will respawn and a horde will come for the survivors.

The survivors must survive the horde by killing all the zombies.

The round is won when all zombies are killed while the bomb is planted.

The game was eventually published in 2008, and the rest is history.

you could find the modhere.