Does "dangerous knowledge" exist and are there areas of research that should be "off limits"?

In 1905 as part of his description of the special theory of relativity, Albert Einstein noted that a small amount of matter could release a tremendous amount of energy (E=mc2). Years later, that became the foundation for the atomic bomb. More recently in 2001, scientists deliberately made the mousepox virus more lethal to mice by introducing a protein that suppresses the immune system. This created quite a controversy at the time since the study could be easily replicated in the human pathogen, smallpox. Thus, some studies are obviously fraught with danger (like the later one), while others have major, benign implications that years later are appropriated for different purposes. Should all research be allowed under the premise that we cannot control it or know what the imlications might be decades later? If you support controls, then who decides what can pursued and what cannot?