The Dark Zone is a walled-off quarantine zone in Manhattan. When the pandemic hit, the authorities gathered the sick in this area and brought in the best scientists and medical equipment to try to contain the virus and look for a cure.
In the Dark Zone, players can chose to collaborate or attack other Division agents. Once you attack other players, you are “flagged” as a Rogue agent and become valuable bounty for normal agents. Once marked, your watch and antennae turn red. From there, you need to stay alive until your rogue counter is up and you turn back to normal. However, if you attack a rogue agent, you will not be flagged, but get the reward for killing them.