It only looks nasty because it was all over everything, I don't have anything against Nutella at all.
I actually just had a similarly nasty experience with catfood -- one of the cans exploded, and smelled to high heaven when I got home today (I received it last week some time, and it had exploded probably during packing -- not even shipping, the box was fine).
And it, too, looked nasty.
EDIT: So nasty -- it had started to mold, that's what I was smelling. Hairy like a caterpillar mold. (involuntarily shudders)