I think most railfans have plenty to worry about already, and don't need to worry too much about this.
But some of us are paid to worry, and also do something about it. It would be extremely difficult to directly tamper with an electronic interlocking per se, so as to produce false clears or conflicts. So difficult in fact that no one would bother, especially since there are much easier ways to cause trouble. I won't go into much detail here in public, but the most serious weak spot is in proposed CTBC systems using data radio.
But already, the AREMA CBTC (PTS) committees are aware, and are working hard on it - especially about how to absolutely prove data radio identity, before any train can act upon any transmitted command. Basically, if you can't absolutely prove the identity of source of the data, the most restrictive condition will be assumed until proven otherwise. Not a lot different than now.
Spoofing signals is not at all new. It has not been very common, but it has already happened, the most famous time being in 1963. See the link below - to see how easy that already is now. After the AREMA committees get done, radio based systems will be much more secure than things are now with actual physical signals.
Great Train Robbery