What does the woman mean?

M: I was shocked when I heard you had finished your research project a whole month earlier.
W: How I managed to do it? It’s still a mystery to me.

W: Why are you so upset, David?
M: My boss warned me not to spend all day communicating with my friends, but I didn’t. He just didn’t believe me.
W: You must have forgotten to close your hot mail’s window again. You should have known better.