The topic of dual-use in research is something that is not often brought up. The term "dual-use" refers to research whose purpose is to advance the understanding of a particular subject, but whose methods or results simultaneously bear the potential for malicious or unintended use. Perhaps the best example of such research is that of atomic energy; while understanding how to capture nuclear energy has provided substantial benefits, misuse of this information can lead to the development of an atomic bomb by anyone capable of applying this knowledge.
Indeed, Albert Einstein once said, \The release of atom power has changed everything except our way of thinking...the solution to this problem lies in the heart of mankind. If only I had known, I should have become a watchmaker.\" Though not directly referring to dual-use, it appears to me that while he realized that this was a tremendous discovery of knowledge, it had also the potential of dual-use.
As would be expected the problem of dual-use research is not just limited to physics and atomic energy -- another example presents in microbiology. The growing understanding of the pathomechanics behind disease transmitting vectors, such as viruses and bacteria, may be misused in the form of bioterrorism. For instance, studies that seek to understand how viral surface markers continue to evolve over years to cause disease may provide an opportunity for misuse to create stronger viruses, but are likewise necessary for creating defense against such pathogens.
Though a little off-topic, It may be worth pointing out the irony, that the sheer potential of bioterrorism has lead to research that would not likely have been conducted otherwise. Take the Ebola virus for example - the virus, though very deadly, has not caused any deaths in the U.S., and has been limited to ~1000 cases since its first recorded outbreak. However, research continues on vaccines and understanding its pathomechanism, largely because of its bioweapon potential.
The discussion of dual-use is sure to rise as we continue to create "synthetic" bacteria and viruses, as we may be simultaneously creating a framework for others to exploit such techniques to do harm.