Missile silos aren't "in" military bases as we normally tend to think of them. The silos themselves are usually sited in remote locations, the surfaces are often unguarded and protected only by chain-link fence.

https://en.wikipedia.org/wiki/File:Active_LGM-30_Minuteman_S...

http://countrychickengirl.blogspot.com/2011/03/sunday-drive....

...with all sorts of drones / driverless cars around nowadays, you can imagine some of them could be remotely hacked and made to land or park themselves more or less inconspicuously atop a silo at the right time. You don't need to "hack a silo" (which, I hope, is really not possible!) anymore to incapacitate the adversary from delivering a nuclear strike, just hack any random device that can be moved around at the right time. Hopefully you can't use the same tricks to trigger a missile launch, so overall the new situation might have increased humanity's chances of long term survival :)

Now it would be obvious, but in a future with god knows how many small little e-critters swarming around everywhere doing god knows what... yeah, bad I idea to share, but someone in a foreign military paid to have such an idea would've already had it anyway :)

I'm guessing the physical security around a missile launch silo is likely to prevent that.