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According to several posts on Batman: Arkham City's official forums, users are experiencing a bug that causes their Xbox 360 save files to be deleted without warning. In an ongoing thread, many users report dozens of hours of progress lost thanks to the bug. 

The problem appears to be specific to the Xbox 360 version of the game, and reports range from six hours of progress lost to save files that were 80% complete. Some users have speculated that the problem may be related to the Catwoman DLC pack, though that hasn't been confirmed. 

These reports are unverified for now, though an increasing number of them have continued to appear since the game's launch in October. We've reached out to Warner Bros. and will update this story with any comment we receive. 

{IGN}