  Online social networks provide a platform for sharing information and free
expression. However, these networks are also used for malicious purposes, such
as distributing misinformation and hate speech, selling illegal drugs, and
coordinating sex trafficking or child exploitation. This paper surveys the
state of the art in keeping online platforms and their users safe from such
harm, also known as the problem of preserving integrity. This survey comes from
the perspective of having to combat a broad spectrum of integrity violations at
Facebook. We highlight the techniques that have been proven useful in practice
and that deserve additional attention from the academic community. Instead of
discussing the many individual violation types, we identify key aspects of the
social-media eco-system, each of which is common to a wide variety violation
types. Furthermore, each of these components represents an area for research
and development, and the innovations that are found can be applied widely.
