Software is continually evolving, to improve performance, correct errors, and add new features. Code modifications, however, inevitably lead to the introduction of defects. To prevent the introduction of defects, one has to understand why they occur. Thus, it is important to develop tools and practices that aid in defect finding, tracking and prevention. In this paper, we propose a methodology and associated tool, Herodotos, to study defects over time. Herodotos semi-automatically tracks defects over multiple versions of a software project, independent of other changes in the source files. It builds a graphical history of each defect and gives some statistics based on the results. We have evaluated this approach on the history of a representative range of open source projects over the last three years. For each project, we explore several kinds of defects that have been found by static code analysis. We analyze the generated results to compare the selected software projects and defect kinds.