In the future Smart Grid, Phasor Measurement Units (PMUs) will monitor the power grid state in real-time by synchronizing measurements across the network using GPS. However, because civilian GPS is unencrypted, PMUs are susceptible to spoofing. This webinar presents a spoofing detection algorithm using a wide-area, hybrid communication architecture: Each PMU securely transmits conditioned signal fragments containing the military P(Y) signal, which serves as an encrypted signature in the background of all authentic GPS signals. This signature is then verified amongst several, distant receivers, strategically picked with a subset selection algorithm. The algorithm has been demonstrated to successfully evaluates the authenticity of a widely dispersed receiver network, using real- world data recorded during a government-sponsored, live-sky spoofing event.