Kurt Thomas on Security at Twitter and Everywhere by Marti Hearst.
From the post:
Kurt Thomas is a former Twitter engineer and a current PhD student at UC Berkeley who studies how the criminal underground conspires to make money via unintended uses of computer systems.
Focus is on underground economies that depend upon theft of data or compromise of access to data.
Suspect if you started making money over a free service, that would be an “unintended use” as well.