What is this defense called?

And what's a good way to exploit it? I played 3. d4...exd4  4. Nxd4.

This is the Damiano Defense. Your d4 is a very good move. So is Bc4. The sharpest line and generally the published refutation is Nxe5. ie...

Worth noting that Black can only protect his pawn on e5 through using his Queen to threaten tactics on e4. The pawn on f6 contributes nothing to its defense, and inhibits his development, and weakens his kingside pawn structure. It only does bad things.

It arises from beginner logic like "I want to reinforce my e pawn but don't want to block my bishop. It could be like a kingside slav".

Thanks a lot. I haven't seen this defense much before, but found it gave me an easy control over the center.