I was confused by Pandorum's ending?

it was a good movie, but I didn't understand what was going on with the creatures. Dont want to give it away so let me say spoiler alert right now. Are the creatures former crew members that became cannibals years ago? Did they come from space? Did they come from the planet? And if they did, arent they going to still be a threat to the survivors? Or were the creatures all a result of pandorum and never existed. I was getting that idea when they thought the creatures were breaking into the bridge.