Infected Lab X is a one mission campaign for Alien Swarm made by Herezy. This is a map into an underground laboratory, your squad need to find the exit, but be careful, aliens are every where, and there are some ambushes. This version has all files inside VPK renamed not to conflict with other addons, the nodegraph is fixed, and some spawners are adjusted not to spawn aliens on top of marines' heads.
How to install campaign\map addon?
Automatic.(not recommended) Extract the VPK addon file from the archive and double click it. The Steam Addon Installer will install it and display a dialog window which says "Addon *** was successfully installed." This method is not recommended because Addon Installer can corrupt addon(VPK) file name. This way after automatic installation you can have a file EXTERM~.VPK instead of extermination.vpk into your "addons" folder.
Manual.(recommended) Extract the VPK addon file from the archive and copy it into your "addons" folder:
C:\Program Files\Steam\SteamApps\common\alien swarm\swarm\addons\
C:\Program Files (x86)\Steam\SteamApps\common\alien swarm\swarm\addons\
Restart the game after installing.