Achievement Description; Kill 5,359 Infected in the Crash Course campaign.


Disclaimer:The guide requires you to use some of the console commands that the source engine provides;
There are 2 methods I've coined; Executing a command string by either creating a config (.cfg) file or running it in the console. I'd advise you the former in order to speed up the process, and it seems to be a lot more stable. Alternatively you could do the latter which is equivalent, but by doing so my pc crashed twice. It's up to you to choose which method you want, for you one method might work better than the other.
Keep in mind This guide involves a famous exploit for old source engine games. By enabling and disabling the in-game cheat commands in the same string (sv_cheats 1; ...; sv_cheats 0) tricks the game into allowing any command executing in between.
If you haven't already enabled the console navigate:
Options->Keyboard/Mouse-> ALLOW DEVELOPER CONSOLE

Go to <steam install directory>/steamapps/common/left 4 dead/left4dead/cfg
Create a txt file and name it however you want; iI chose mine as "spam_horde"
Add the following code:
Rename the .txt file as a .cfg file and you're done.
When executed, the .cfg file will:

• Kick all bots so that you'll get all the kills
  
• Increases the limit of zombies spawned by horde
  
• Increase the number of zombies spawned by a horde
  
• Give you the hunting rifle- If you wish to choose any other weapon you could change the command to one of the following:
  Rifle: give rifle Shotgun; give autoshotgun Hunting Rifle: give hunting_rifle
• Spawn a "Mob", which is supposedly a larger horde
  
• Replenish yourself with a new weapon, so you won't run out of ammo
  
• Bind the command string to the button "b" (randomly chosen, could choose any button you want) so whenever you see the "mob" has ended you could start a new one.

Open the console and type:
You'll start an offline campaign of "Crash Course" on the second part (Truck Stop Finale).
A word of advise: You should stay inside the saferoom at all times.
If you spawn as the character of your choice (e.g. Bill for my config) you're good to go.
If not, type Open the console and type:
So now whenever you press the button "B" you run the cfg you created earlier. Of course it's up to you to choose which button to bind, I randomly chose B. A lot of continuous hordes will occur and you'll keep killing the zombies from the inside of the saferoom. Keep in mind that the safehouse door is unbreakable in L4D1. The great thing about this method is that it seems to handle much more zombies in the mobs and it did not crash for me at all.

Open the game and type in the console:
You'll start an offline campaign of "Crash Course" on the second part (Truck Stop Finale). A word of advise: You should stay inside the saferoom at all times.
So now that you're in-game you should open the console again and type:
Where X, Y, Z the survivors that are controlled by the bots. (e.g. if you spawn as Bill, kick Francis, Zoey and Louis).
The upper string of commands will run the same commands as with Method 1, by pressing the binded button "b" of course.
I decreased the amount of zombies spawned i nthe mob because the game crashed twice with higher amounts of zombies. It could be a coincidence of my pc slowly aging, but do as you wish.

And that's how you do it folks. In 5 minutes I managed to get around 500 kills with the 1st method. So it is possible to get the achievement in an hour or so. That's a valid way to get the ZOMBIE GENOCIDEST achievement as well. If you encounter any problems write it down in the comment section. And don't forget: The Mob Rules!