The Internet of Things (IoT) demands tailor-made security solutions. Today, there are a number of proposals able to meet IoT's demands in the context of attacks from outsiders. In the context of insiders, however, this does not hold true. Existing solutions to deal with this class of attacks not always take into consideration the IoT's idiosyncrasies and, therefore, they do not produce the best results. This work aims at coming up with tailormade security schemes for thwarting attacks from insiders in the context of IoT systems. Our solution makes use of a pioneering solution to pinpoint vulnerabilities: we crosscheck data from communicating nodes. It provides the same guarantees as traditional security mechanisms, but it is about 83% more efficient, according to the experiments that this article describes.