Originally Posted by markpjd
Not sure, seems to be some kind of microscopic mold spore.. I always thought mold needed a food source, but I don't know the science behind it all. What doesn't make sense is that I had some disks stored in almost perfect condition and they still failed due to mold. On the other hand, I think it may be brand dependent too, as some disks seem more resistant or durable than others.
As long as there is more than 50% humidity in the air, mold can grow on a substrate. Unless you actively control humidity there are always moments where humidity will be above 50%.