  Stack Overflow incentive system awards users with reputation scores to ensure
quality. The decentralized nature of the forum may make the incentive system
prone to manipulation. This paper offers, for the first time, a comprehensive
study of the reported types of reputation manipulation scenarios that might be
exercised in Stack Overflow and the prevalence of such reputation gamers by a
qualitative study of 1,697 posts from meta Stack Exchange sites. We found four
different types of reputation fraud scenarios, such as voting rings where
communities form to upvote each other repeatedly on similar posts. We developed
algorithms that enable platform managers to automatically identify these
suspicious reputation gaming scenarios for review. The first algorithm
identifies isolated/semi-isolated communities where probable reputation frauds
may occur mostly by collaborating with each other. The second algorithm looks
for sudden unusual big jumps in the reputation scores of users. We evaluated
the performance of our algorithms by examining the reputation history dashboard
of Stack Overflow users from the Stack Overflow website. We observed that
around 60-80% of users flagged as suspicious by our algorithms experienced
reductions in their reputation scores by Stack Overflow.
