For a while, Ubisoft wasn't sure if it was possible to finish ZombiU on survival mode, with the development team only completing it mere days before the game was finished.
Ubisoft may have underestimated gamers. ZombiU has only been available in the US for just over a week, and it looks like the game has already been beaten on the hardest difficulty available.
Kotaku has pointed out that a gamer by the name of MTang19 has beaten the mode, taking a screen capture of a congratulatory message to MTang19 from Ubisoft in the game:
Stealth Gamer however, has reported that ChristmasGT, Moitar, Taikoubou22, Cullen, DeDeDe, GAMERatHEART, neetloaf and ZombieCakez, had all beaten the game on survival mode before MTang19.