Users of social networking sites post more and more materials that may be subject to copyright and related rights. As a result, these activities quite often constitute a breach of law. The article describes what activities – carried out as part of the functionality of social networking websites – can result in copyright infringement. The analysis covers not only the issue of posting a specific material protected by copyright on the website by its user, but also subsequent activities consisting in making the material available (re-posting) by providing reference (hyperlinks). The author puts forward a hypothesis that in some cases not only the person who places material on a social networking website but also the person who makes the material available by posting a hyperlink to it is liable for the infringement of copyright.