Its called GPS spoofing.The Department of Transportation (DOT) has warned that the civilian GPS signals (the only ones available to most government users and all private users) are not secure. Few GPS users are paying attention.GPS spoofing is a extreme threat to national security. But it can easily be solved.
I agree that is a problem, but I also think China may have cracked some direct up and down links used for C3. That could give them direct flight control and possibly functional systems control.