Why it is hard to fight against cyber criminals?

We are witnessing numerous cyber attacks every day, however, we do not see many cyber criminals are brought to justice. One reason is that it is technically hard to identify and trace cyber criminals. One reason for this passive situation is our limited or even inappropriate understanding of the cyber space. In this paper, we survey the challenges and opportunities in this research field for interested readers. We also list promising tools and directions based on our understanding.<br />