Blu-ray discs, described by many as "disc rot" due to the mould-like spots that have made several owner's Blu-ray discs unplayable. The five page thread has reports from dozens of forum members, many of them discovering spots which can't be rubbed off on Blu-ray versions of "The Prestige." It's impossible to judge how widespread the problem is from a single forum thread, although it's not unheard of to see a product recall after a problem is discovered by users on a forum. It's also worth noting that for every user that has reported the spots, there's one or more people with discs that have no problem. If you've encountered the same issue, your best policy is to try and get a refund / replacement disc from the place where you originally bought it from. If enough people are reporting a problem, then retailers will be a much stronger voice than a bunch of consumers sounding off in the echo chamber that is "the internet."