This work proposes a new and flexible unreliable failure detector, denoted Impact Failure Detector (FD), whose output gives the trust level of a set of processes. By expressing the relevance of each node by an impact factor value as well as an acceptable margin of failure in the system, the Impact FD enables the user to tune the failure detection configuration in accordance with the requirements of the application: in some scenarios, the failure of low impact or redundant nodes does not jeopardize the confidence in the system, while the crash resulting from a high impact factor may seriously affect it. Either a softer or stricter monitoring is thus possible. Performance evaluation results using real PlanetLab [1] traces confirm the degree of flexibility of our failure detector and that, due to the margin of failure, the number of false responses may be reduced when it is compared with traditional unreliable failure detectors.