Online hate speech and discrimination, copyright violation, non-consensual and child pornography, exchange of information for terroristic purposes are just some of the phenomena that often occur in online groups, closed or open, which are frequently difficult to identify and to deal with. These groups are managed by one or more subject who can control the key aspects, choose the topics, moderate and manage discussions and shared material. What are the responsibilities? Are there any possibilities to remove or limit the sharing? These are the topics covered by the talk, that will help us to understand the legal and technical issues raised by the creation, management and participation in these online groups.