"Darknet platforms and their growing popularity present unique challenges to cybersecurity. Blocking all Darknet traffic is difficult and often unduly burdensome for many system operators. Command-and-Control (C2) servers hosted on the Darknet are difficult to uncover and shutdown, making the Darknet an attractive haven. The proliferation of stolen credentials on Dark Web markets leave systems vulnerable, even if systems have secure networks."
Department of Homeland Security: http://www.dhs.gov/