TCAS isn't built off of ADS-B (it existed long before ADS-B was ever conceived), but it's the same basic idea (mode c / mode s transponders) and probably has th

TCAS isn't built off of ADS-B (it existed long before ADS-B was ever conceived), but it's the same basic idea (mode c / mode s transponders) and probably has the same theoretical security vulnerabilities. There's a pilot at the controls so that the technology doesn't have to be perfectly secure. If you want to walk around broadcasting fake ADS-B or Mode C signals, someone will probably find you in hours, and the only effect it will have is maybe reducing the throughput of the busiest airports if the weather happens to be particularly marginal that day.