With technological progress, knowledge about the possibilities and ways of misuse of personal data has advanced. As much as they are protected by the laws of the Republic of Croatia and state authorities, personal data are never completely safe. They are used, collected and processed every day, both in the everyday and in the virtual world. The manner in which it will be processed and the rules for preserving the personal data of all people are also determined by law. One of the greatest dangers is represented by people who, in various ways, try to commit criminal acts against other people and their personal data. Cyber attacks are an increasingly common phenomenon on the Internet. Children, as well as adults, can be at risk on sites that do not ensure privacy, where they can publish important information that can be misused. This paper provides a definition of the term personal data, describes the ways of their use on the Internet and the laws that protect them in the Republic of Croatia. Dangers that can harm personal data and ways to protect them are also listed. Furthermore, the results of the conducted research on the development of future teachers' awareness of the protection of personal data on the Internet are described. The research was conducted using a questionnaire that was filled out by 101 students of the Teacher Training College in Osijek. The obtained results show that the majority of future teachers are aware of the danger, and most believe that their data is not safe on the Internet. The results also show that 55.4% of future teachers believe that they have sufficient knowledge and competence to teach elementary school students about personal data protection on the Internet.