The first scenario outlined is completely redacted, illustrating the acute sensitivity about the issue. The second scenario is heavily blacked out but, according to the memo, "would be both logistically and technically challenging for a non-state group to undertake".
A third, also heavily redacted, scenario "constitutes the most technically challenging of the scenarios considered here".
Concerns that terrorist groups might look to "weaponise" Ebola have been raised by several think-tanks and politicians. Last year Francisco Martinez, Spain's state Secretary for Security, claimed that Isis fighters were planning to carry out "lone wolf" attacks using biological weapons. Martinez said that his belief was informed by listening in to conversations uncovered in secret chatrooms used by terrorist cells. The claim has since been played down by others.
Jeh Johnson, the US Department of Homeland Security Secretary, said last October that "we've seen no specific credible intelligence that Isis is attempting to use any sort of disease or virus to attack our homeland".
Dr Filippa Lentzos, a senior research fellow at King's College London and an expert on bioterrorism, said terrorists looking to use the virus as a weapon would encounter problems.
"It doesn't spread quickly at all. Terrorists are usually after a bang and Ebola isn't going to give you that."
Q & A
Could other biological weapons be more attractive to terrorists?
Unlike Ebola, which requires the transmission of body fluids, anthrax spores can be dried and milled to form tiny particles that can be inhaled.
Have pathogens been used as a weapon before?
Following the attacks in New York and Washington in 2001, five people died in the US after opening letters laced with anthrax.
Is there concern that terrorists are becoming increasingly inventive?
One scenario could see terrorists combining genes from different pathogens to synthetically create super pathogens that could spread disease more effectively than Ebola. But expert Dr Filippa Lentzos suggested this was unlikely. "It's pretty damn hard to make dangerous pathogens from scratch in the lab. At this point I'm not sure that's what we need to worry about."
— Observer