And the experts say ” The real shocker is that U.S. rivals do not face this vulnerability. China, Russia and Iran have terrestrial backup systems that GPS users can switch to and that are much more difficult to override than the satellite-based GPS system. The U.S. has failed to achieve a 2004 presidential directive to build such a backup.”

For the complete story : https://www.scientificamerican.com/article/gps-is-easy-to-hack-and-the-u-s-has-no-backup/

https://www.scientificamerican.com/article/gps-is-easy-to-hack-and-the-u-s-has-no-backup/