A new map has been released, Blood Harvest! Servers will go down immediately. Update details bellow.
Taken from Steam News:
Updates to Left 4 Dead 2 have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:
Death Toll campaign released
Fixed scoring in finaleBlood Harvest; The Bridge
Infected will spawn in front of the survivor team on their way to the Safe House.
Added Infected spawn locations on the hill by the Safe House.Blood Harvest: The Train Station
Fixed exploit that allowed Infected team to trigger the onslaught.