  Research into influence campaigns on Twitter has mostly relied on identifying
malicious activities from tweets obtained via public APIs. These APIs provide
access to public tweets that have not been deleted. However, bad actors can
delete content strategically to manipulate the system. Unfortunately, estimates
based on publicly available Twitter data underestimate the true deletion
volume. Here, we provide the first exhaustive, large-scale analysis of
anomalous deletion patterns involving more than a billion deletions by over 11
million accounts. We find that a small fraction of accounts delete a large
number of tweets daily. We also uncover two abusive behaviors that exploit
deletions. First, limits on tweet volume are circumvented, allowing certain
accounts to flood the network with over 26 thousand daily tweets. Second,
coordinated networks of accounts engage in repetitive likes and unlikes of
content that is eventually deleted, which can manipulate ranking algorithms.
These kinds of abuse can be exploited to amplify content and inflate
popularity, while evading detection. Our study provides platforms and
researchers with new methods for identifying social media abuse.
