Mac users, beware! Your super private incognito mode, or actually anything you might be doing that you don't want other eyes to see, might not be that safe after all. At least if those eyes belong to other people you allow to use your Mac. A report over the weekend revealed how Apple's computers sometimes suddenly pops up a "ghost" of a previously closed window, potentially revealing its contents. At first, it was NVIDIA's GPUs were theorized to be the culprit, as it is the one handling the graphics work. NVIDIA, however, says it's Apple's OS X that's at fault.