Before a Wireless Sensor Network (WSN) can be used in practice it must be ensured that the WSN can be operated securely. The WSN must be able to handle and withstand attacks. However, the threat to a WSN is generally not constant. The threat situation may differ from one application scenario to the next and threat levels change over time. Therefore, it is necessary to use adaptive security mechanisms that can be tailored to the currently experienced threat level. To allow for such adaptation it must also be possible to monitor and identify the current threat level. The goal of this research project is to develop a risk management strategy for WSNs comprising adaptive security mechanisms and threat monitoring methods.