SETI, unexplained signals
Over the past few decades, many intriguing signals have been picked up by the various SETI programs which are compatible with an artificial origin but remained unidentified. Of these, the most famous is the Wow! signal. Although in the majority of cases, the possibility of interference cannot be ruled out these anomalous sources tend to be concentrated toward the plane of the Milky Way, as would be expected if they were galactic in origin.