We consider Global Navigation Satellite Systems (GNSS) spoofing attacks and devise a countermeasure appropriate for mobile GNSS receivers. Our approach is to design detectors that, operating after the signal acquisition, enable the victim receiver to determine with high probability whether it is under a spoofing attack. Namely, the binary hypothesis is that either the GNSS receiver tracks legitimate satellite signals, ℋ0, or spoofed signals, ℋ1. We estimate power and angle of arrival (AOA) of received signals. A key assumption on the attacker sophistication: Spoofed signals come from one signal source, typically the attacker radio, instead of multiple sources, the satellites, for legitimate signals. We analyze and compare the detectors performance and we derive some lower bounds on the estimation quality for unknown parameters. Based on the simulation results, the detectors can operate on low SNR that is applicable for GNSS.