  Abusers increasingly use spyware apps, account compromise, and social
engineering to surveil their intimate partners, causing substantial harms that
can culminate in violence. This form of privacy violation, termed intimate
partner surveillance (IPS), is a profoundly challenging problem to address due
to the physical access and trust present in the relationship between the target
and attacker. While previous research has examined IPS from the perspectives of
survivors, we present the first measurement study of online forums in which
(potential) attackers discuss IPS strategies and techniques. In domains such as
cybercrime, child abuse, and human trafficking, studying the online behaviors
of perpetrators has led to better threat intelligence and techniques to combat
attacks. We aim to provide similar insights in the context of IPS. We
identified five online forums containing discussion of monitoring cellphones
and other means of surveilling an intimate partner, including three within the
context of investigating relationship infidelity. We perform a mixed-methods
analysis of these forums, surfacing the tools and tactics that attackers use to
perform surveillance. Via qualitative analysis of forum content, we present a
taxonomy of IPS strategies used and recommended by attackers, and synthesize
lessons for technologists seeking to curb the spread of IPS.
