Modern processors embed features such as pipelined execution units and cache memories that can hardly be controlled by programmers through the processor instruction set. As a result, software-based fault injection approaches are no longer suitable for assessing the effects of SEUs in modern processors, since they are not able to evaluate the effects of SEUs affecting pipelines and caches. In this paper we report an analysis of a commercial processor core where the effects of SEUs located in the processor pipeline and cache memories are studied. Moreover, the obtained results are compared with those software-based approaches provide. Experimental results show that software-based approaches may lead to errors during the failure rate estimation of up to 400%.