  Recently, Unmanned Aerial Vehicles (UAVs) are employed for a plethora of
civilian applications. Such flying vehicles can accomplish tasks under the
pilot's eyesight within the range of a remote controller, or autonomously
according to a certain pre-loaded path configuration. Different path deviation
attacks can be performed by malicious users against UAVs. We classify such
attacks and the relative defenses based on the UAV's flight mode, i.e., (i)
First Person View (FPV), (ii) civilian Global Navigation Satellite System based
(GNSS), and (iii) GNSS "plus" auxiliary technologies (GNSS+), and on the
multiplicity, i.e., (i) Single UAV, and (ii) Multiple UAVs. We found that very
little has been done to secure the FPV flight mode against path deviation. In
GNSS mode, spoofing is the most worrisome attack. The best defense against
spoofing seems to be redundancy, such as adding vision chips to single UAV or
using multiple arranged UAVs. No specific attacks and defenses have been found
in literature for GNSS+ or for UAVs moving in group without a pre-ordered
arrangement. These aspects require further investigation.
