Research on trolls is scarce, but their activities challenge online communities; one of the main challenges of the Wikipedia community is to fight against vandalism and trolls. This study identifies Wikipedia trolls' behaviours and motivations, and compares and contrasts hackers with trolls; it extends our knowledge about this type of vandalism and concludes that Wikipedia trolls are one type of hacker. This study reports that boredom, attention seeking, and revenge motivate trolls; they regard Wikipedia as an entertainment venue, and find pleasure from causing damage to the community and other people. Findings also suggest that trolls' behaviours are characterized as repetitive, intentional, and harmful actions that are undertaken in isolation and under hidden virtual identities, involving violations of Wikipedia policies, and consisting of destructive participation in the community.