Scientific workflows have recently emerged as a new paradigm for representing and managing complex distributed scientific computations and data analysis, and have enabled and accelerated many scientific discoveries. Many scientific workflows are distributed and collaborative as they result from some collaborative research projects that involve a number of geographically distributed organizations. In these workflows, information flow control becomes a key security problem. In this paper, we propose to model a scientific workflow using a hierarchical state machine and present techniques for verifying and controlling information propagation in scientific workflow environments based on hierarchical state machines. To the best of our knowledge, this is the first effort for information flow analysis in the area of scientific workflows.