So either this was a security breach, a human mistake or a psyops/test on a small isolated American population. In the first case, we'll probably only be told about it if they actually make an arrest and the system is patched. The second is an interesting case, we'll come back to. The final one: it was intentional and used to track what happened on the islands, and to also watch that information propagate back to the…
Ok, but what would be the point of that?
You would either discover that people are terrified of nuclear war, in which case... you can't do anything useful with that information. Or, you'd discover that people don't respond to the message, in which case... you can't do anything with that information.
Why would anyone who wasn't a particularly stupid villain intentionally do this?