If I were you, I'd google for pictures of a porous egg. I'm guessing that's the spots you are seeing. If it does not look like a porous egg and the spots are dark rather than light, it's probably a bacteria and I'd throw it out. You definitely want to look at pictures to determine which it is though, because porous eggs can hatch, but rotten ones can explode. I'm incubating my first batch of eggs, and I have some porous ones, and I just threw out a rotten one.
If it is speckled and something is inside it don't toss it!! (throw it away) All of my eggs were speckled and they all of them except 1 hatched! The one that didn't I already new wasn't gonna hatch because it had a lot of stuff on it so I think bacteria got in it. So if it is speckled don't give up!!