Valve has confirmed that Dead Center and Hard Rain are a pair of campaigns from Left 4 Dead 2 following yesterday's leak.
"They are from the game," marketing director Doug Lombardi confirmed to Eurogamer in an email.
Elsewhere, the game's Achievement list has popped up (thanks Kotaku), also mentioning the campaigns, and offering a glimpse not only of the way Valve plans to keep you coming back, but perhaps also a few unannounced bits and pieces.
These may constitute spoilers for some, so steer clear if you want it all to be a surprise.
For example, there's talk of collecting "vials of Boomer vomit from infected CEDA agents", and a "bile bomb". The two may be linked, although there's no direct word on that.
Valve's whimsical sense of humour is also in evidence, with 60 extra gamerpoints tied up in the Dark Carnival campaign for outwitting "Moustachio" (he's a nut) and rescuing "Gnome Chompski".
Check out our recent Left 4 Dead 2 hands-on with Swamp Fever and Dark Carnival campaigns to find out why we're rather excited about the game's November launch.