Since the show doesn't exactly specify where the virus originated, fans are totally left guessing.
So, to give you a warning on what this ongoing disease/villain entails, check out this scoop we've learned via TV Guide:
You will be surprised to see how far this illness will spread. "There's a point where the number of able-bodied people is one or two," Lauren Cohan tells me. "It gets to a point where Maggie is the only person who can actually fight."
'The Walking Dead' airs every Sunday on AMC.