This report presents recommendations on detection of jamming and spoofing attacks on GNSS receivers are given. The purpose is to detect the attack before the navigation system is affected. A coarse classification of different types of jamming and spoofing attacks as well as methods of detecting these are given. For a stand-alone GNSS receiver it is recommended that energy detection in combination with a control of the plausibility of the existing navigation data is used. The use of an encrypted signal and an antenna array will increase the possibility to detect jamming and spoofing attacks. A navigation system consisting of several GNSS receivers and/or other sensors should use the additional information to further minimize the probability that a jamming or spoofing attack could be performed unnoticed.