Anonymity services reduce the amount of information available that can be used to track an adversary's activities. Multiple options are available to hide activity, limit tracking, and increase anonymity.  
Detectable by Common Defenses (Yes/No/Partial): No
Explanation: Depends on service. Some are easy to detect, but are hard to trace (e.g., [https://torproject.org TOR]).
Difficulty for the Adversary
Easy for the Adversary (Yes/No): Yes
Explanation: Easy access to anonymizers, quasi-anonymous services like remailers, [https://torproject.org TOR], relays, burner phones, etc.
- Roger Dingledine, Nick Mathewson, Paul Syverson. (2004, August). Tor: The Second-Generation Onion Router. Retrieved March 28, 2017.
- Sean Gallagher. (2012, March 6). Inside the hacking of Stratfor: the FBI’s case against Antisec member Anarchaos. Retrieved March 1, 2017.