Recent years have seen the proliferation in our skies of flying drones otherwise called UAVs (Unmaned Aerial Vehicle). Their current and potential uses are many: from the military uses to leisure activities through business applications like photography, aerial imaging, spotting, pest extermination (like hornets nest), home delivery, etc. This was made possible and facilitated by the miniaturization and the reduction of the power consumption of Microelectromechanical Systems (Mems), but also by the dissemination of techniques making the navigation easier. We refer of course to satellites geolocation techniques such as the well-known Global Positioning System (GPS) and Global Navigation Satellites Systems (GNSS), which is its extension to all existing constellations. The growing interest in UAVs is obvious, however, this brings some questionings: are there any limits to what a drone can do? This article aims to put the problematic of the drone linked to the vulnerability of the GPS signal and its consequences. Indeed, one of the characteristics of civilian GNSS signals (therefore free to use) is their very low power. A GNSS receiver is therefore easy to decoy by means of a fake GNSS signal that reproduces the aspect of a real signal but contains false positioning information. Under these conditions, the GNSS receiver embarked by the drone calculates a position which is not the real position. Consequently, the trajectory of the drone is distorted. We will see, from a theoretical point of view, what happens when a receiver is submitted to a fake signal and the consequences that this induces to the navigation of the drone. Simulations will support our words and laboratory tests on existing UAV navigation systems will be presented