This paper deals with the increasingly present and widespread problems of privacy violations and misuse of personal data of social network users, with a focus on their appearance in the field of politics. The paper studies the ways of using personal data of social network users and briefly explains who has access to this data. For this purpose, the concepts of privacy protection, i.e. protection of personal data in the member states of the European Union and in the United States of America are also explained. The paper also examines why it is necessary to critically analyze practically all information that reaches numerous users of social networks, why disinformation and fake news mostly circulate on social networks and how they can be used as a dangerous political weapon. The well-known Cambridge Analytica case, i.e. the involvement of that British analytical company in two globally important political events in 2016: the presidential elections in the USA and the referendum for Great Britain's exit from the European Union, or "Brexit", was used as the main case study for this work's research. It is explained how the mentioned company, in violation of Facebook's terms of service, collected the personal data of many Facebook users and how voters in the mentioned countries were manipulated with targeted communication and a special advertising method. Through this case, it is also shown how such and similar moves can influence the outcomes of certain political events and threaten the democratic systems of individual countries.