It appears that Aliens: Colonial Marines is nuking Xbox 360 saves from orbit.
Just in case Aliens: Colonial Marines wasn't quite enough of a dropship wreck already, here's another log on the fire. According to several reports posted on the Gearbox forums, owners of the Xbox 360 version of the game are randomly losing their saved games. And not just that; campaign progress, player levels, brightness settings and controls schemes are all disappearing. The problem appears to crop up when the game is installed to the hard drive.
Gearbox hasn't commented on the issue at this point but a few victims of the bug theorize that it's an issue with Gearbox servers, since save data doesn't appear to be stored on local systems. If so, it's possible that the lost data could eventually be restored, although forum posts complaining about the bug are dated from February 12 to today, a long time for a server error to go uncorrected.
If you're lucky enough to have dodged the Colonial Marines bullet, this is just one more reason not to get in front of it; if, on the other hand, you dropped $60 on the thing and find yourself forced to start over again from square one, you have my sympathy. Either way, it's an unfortunate mess, but it almost seems appropriate somehow. We've reached out to Gearbox for information and will update if and when we hear back.
Source: Gearbox forums