To be fair, this isn't really _that_ accurate, it's only good to about 10ms, GPS will get you to 0.001ms accuracy, at least with the right kit.

Technically you can broadcast a new time to your neighborhood and have most people late to work (the ones having that kind of clock alarm), it's far from secure and accurate.

That suffers from the same vulnerabilities.

I have trouble picking up WWVB indoors at home even without jamming.