“Click Here to Join”: A Large-Scale Analysis of Topics Discussed by Brazilian Public Groups on WhatsApp

WhatsApp has many similarities with online social networks, as it allows connections between multiple people and massive communication by sharing content with your contacts and public groups, which brings people together to discuss a topic. Even though it is one of the most popular social media in the world, there is a lack of a systematic understanding of the Whatsapp ecosystem, especially when it comes to knowing the subjects discussed in public groups and how other users find/join those groups. In this direction, our goal is to investigate how public groups are shared on the Web and also map the main topics existing within this ecosystem. For this, we perform a large-scale collection, spanning four main sources on the Web for sharing groups, with more than 270k WhatsApp public groups, categorizing and analyzing this environment. Our results shed light on a large existence of groups focused on topics such as friendship, pop culture, stickers, sales, jobs, education, and even adult content suggesting the many uses of the WhatsApp tool. We also found key differences in groups according to the source where it was posted. Moreover, we discovered how group links work to persuade users from other platforms into the underground environment of WhatsApp. Malicious groups abuse its closed architecture and low moderation for illicit practices such as selling fake money and cloned cards. Furthermore, our analysis also found evidence of automated behavior in malicious group sharing. Finally, we discuss implications and measures that can be taken to address these issues.