  Malicious Twitter bots are detrimental to public discourse on social media.
Past studies have looked at spammers, fake followers, and astroturfing bots,
but retweet bots, which artificially inflate content, are not well understood.
In this study, we characterize retweet bots that have been uncovered by
purchasing retweets from the black market. We detect whether they are fake or
genuine accounts involved in inauthentic activities and what they do in order
to appear legitimate. We also analyze their differences from human-controlled
accounts. From our findings on the nature and life-cycle of retweet bots, we
also point out several inconsistencies between the retweet bots used in this
work and bots studied in prior works. Our findings challenge some of the
fundamental assumptions related to bots and in particular how to detect them.
