Not that it really matters what it is, but I'd have to agree with some sort of corrosion. I HIGHLY doubt it's mold. Just because there are favorable conditions doesn't mean mold will grow. Mold still requires a nutrient source for growth and there's nothing very nutritious between the layers of a DVD. And since the pattern is evenly distributed, that would mean the mold was introduced during production meaning that's a pretty filthy production line.

Corrosion? I thought the shiny thing used is aluminum. They don't corrode that easily, does it?

That link, although I didn't read it thoroughly, gave me the impression there's silver in there (why that would corrode any easier I don't know either). I guess I use the term "corrosion" loosely in that due to improper production, something is changing molecular form from what it is supposed to be.

I'm gonna suggest hitting up a chemist to explain it, I'm just a biotechnologist.

I understand that silver does corrode, that's why some CDs in the past uses gold coating to prevent corrosion on the silver. Also I knew that conventional mirror use copper and other substance to protect the silver for the mirror. But as far as I know most CDs and DVDs uses aluminum. But if they does use silver in this case, then it could be an explanation.

By any chance have you ever taken that disc on a flight with you??? I ask because when i moved out of England to where i am now i took my DVDs with me. I remember that a couple of them had major problems after this. The first Terminator DVD became all sticky and generally weird, and another DVD (can't remember what it was off hand) had the same problem as yours...covered in all little black dots. I remember that when i opened the cases for these there was condensation on the DVDs, the storage on the plane for the luggage is obviosuly freezing cold. So thats what caused the problem in my case. Unless you live in a place where the winters are cold and your house doesn't have good heating.

Hope i helped.