Voice over IP services have undergone a large-scale deployment thanks to the development of high-speed broadband access and the standardization of dedicated signaling protocols. They offer new opportunities, in particular in the context of peer-to-peer networks. However they are exposed to multiple security attacks due to a lower confinement in comparison to traditional networks. Protection mechanisms are available, but may significantly impact the service performance. We propose in this paper a risk management strategy for dynamically adapting the exposure of P2PSIP networks. We describe the underlying mechanisms for mitigating risks based on a portfolio of countermeasures. We also detail the mathematical modeling which supports our solution based on the analysis of a case study. Finally we quantify the benefits and limits of this approach through an extensive set of experiments performed with the OMNET++ simulator.