Background: Hackathons have become popular events for teams to work on projects and develop software prototypes. Most existing research focuses on the event itself and on the collaboration of the team that attempts a project while there is limited insight into the evolution of the code that is used and created during a hackathon. Aim: We aim to understand the evolution of the code that is used and created by a team during a hackathon. Specifically, we aim to study to what extent hackathon teams utilize existing code, develop new code during a hackathon, and whether and where the code developed by the team gets reused in other OSS projects. Method: We collected information about 22,183 hackathon projects from DEVPOST – a hackathon database – and obtained further information about the code (blobs), the authors, and the project characteristics using World of Code – a dataset of open source projects. We identified the original authors of the code blobs in the hackathon projects and investigated if these were created before, during, or after the hackathon event. We tracked code reuse by identifying all commits containing the same code blobs which were created by one of the hackathon project members during the event in that project, and all projects which contained those commits. Result: We found that, by volume, most of the code in the hackathon projects is created before the event and by someone other than the hackathon project members, most of which is JavaScript code. Overall, around 28.8% of hackathon code blobs get reused in other projects, with 57.73% of the reused code being used in small projects, 32.85% in medium projects, and 9.42% in large projects. Conclusion: Our study sheds light on the extent pre-existing code is used or new code is created during a hackathon and reused afterwards. Our findings can help to better understand code reuse as a phenomenon and the role of hackathons in this context. Moreover, they can serve as a starting point for further studies in this area.