Crack encryption from the mid 70’s? If there even is any on the Voyager command signal, I couldn’t find a reference to any. But if there is, I’d think modern computers are up to the task.
They’d also either need to be able to generate incredibly strong radio waves through space
My guess is that THIS is the actual security feature.
Not to mention… who would even want to? There’s nothing to gain except slight infamy, if you could even prove you were behind it.