There are many benefits, but also risks related to using the social networks. Among the benefits of social networking belong an easy way to be kept in touch, sharing news, photos, videos and statuses with friends, colleagues, but also meeting new people with similar interests. The risks include, in particular, loss of privacy, misuse of shared records, abuse of personal data, unknown real identity of social network members, and even addiction on social networking.The paper focuses the need to invent a complex tool of prevention in the field of controling the criminality in particular the users of social networks. In the papers is introduced a proposals how to develop a specific prevention tool called "Userfocus". Further, there are described techniques to implement this tool into the social networks. The work comprises a research (questionnaire survey) aimed at users of social networks and their understanding of prevention in social networks. The results showed that the communication (interaction) among social network users is a main reason to actively use those services, loss of privacy is the most negative aspect of social networking, the perceiving of users related to the fight against antisocial networks is mostly negative, they strongly agree with the necessity to apply preventive methods focusing the user of social networks and consider the developing the preventive techniques and their application by competent authorities in prevention of crime on social network.