Update: It most definitely is a zombie outbreak, but it's a multiplayer tweak and not the enigmatic DLC, Rockstar confirms.
A new Eugenics Inc. "ad" has appeared on RockStar Social Club, issuing a vague quarantine order locking down the mysterious company's compound due to a contagious disease outbreak. Eugenics Inc. is a physical location in Grand Theft Auto IV, located in Bohan, though it doesn't play into any part of the game ... yet.
The quarantine announcement is actually the second Eugenics Inc. display to appear on Social Club, following a "Sperm for Cash" ad posted in April (now removed), which, to date, has never been an actual in-game activity. Obviously, Rockstar is proliferating the company's existence for some purpose, right?
Last we heard, Microsoft confirmed the exclusive GTA IV DLC for this fall -- so, any day now. The quarantine posting (unobstructed text after the break) has sparked some speculation that the DLC could be tied to Eugenics' mess. Namely, a potential zombie outbreak! With art assets already in place, what's to stop Rockstar from turning GTA IV into a "28 Days Later" scenario? Keep your eyes peeled.