Security of ADS-B transmissions is improved in a first embodiment to detect position spoofing. The annunciated position source may then be compared with the derived source and a determination is made regarding the difference between the results. Any position difference greater than an amount significantly greater than the combination of the error sources is then a cause for concern and can be used to generate an alert. In a second embodiment, alerting may be based on identification spoofing. From these sources a correlated ID is available which will have an associated confidence based on the number of sources and the level of agreement on the information. Aircraft dynamics may be correlated with the announced ID for consistency. A priori information on the aircraft and location, such as schedule information, and normal operations, may be used to assist in the confidence of aircraft identity. In a third embodiment, alerting may be based on spoofing of identity and position.