It's almost impossible.
So I started thinking about what CIA/DIA priorities might have been, over the last half decade or so, regarding Venezuela, which, indeed, has a virtually unhackable system. What a challenge, eh?, for superclever techies on the wrong payroll!
They've been unable to move Venezuelan voters, who re-elected Chavez again, just before he died, and furthermore gave the rightwing a huge drubbing in the gubernatorial elections, shortly before the special presidential election. No hope there. None of their endless propaganda, none of their USAID funding and "training" of the rightwing, none of the dirty tricks--nothing they tried worked!
I really don't know how they could have done it. But it would surprise me not even a little bit to find out that, a) they had such a project, and b) saw their opportunity, with the death of Chavez, and tried it out on Maduro.
It would have had to be very sophisticated to overcome the Venezuelan paper ballot verification. And Venezuelans are quite vigilant about the verification. They do a whopping 55% automatic audit! (And they've done far more than that, this time--they may have got up to 100%.) That is the stickler. But then, think of all the ferocious, concentrated effort to defeat Chavez, AND the ferocious, concentrated effort of our secret agencies and their corporate allies to control us, and to control the world, with high technology (along with old-fashioned dirty ops like they pulled on Julian Assange).
Anyway, I did say "IF"--IF the CIA did this. I don't have any information that they did, or any clue as to how they could. It is a rock solid system. It really is. It satisfies every criterion for "best election system in the world."
It's just that I don't understand the closeness of the election. I haven't heard any believable explanation for how that could have happened in one week's time.
I also think that the will, within the U.S. government, to destroy the Bolivarian Revolution, is off-the-charts obsessive. They would do ANYTHING for that end, including spending half a decade (since, oh, 2006--Chavez's first re-election, and the second failed coup plot) trying to find the way into Venezuelan's rock-solid election system.
Maduro isn't Chavez. He is not charismatic. But he did nothing during that week to lose 10% to 20% of the voters--voters who had just re-elected Chavez and thrown out most of the rightwing governors! It doesn't make sense. So one's mind casts about for some other explanation. And those who have been furiously plotting against Venezuela's government since at least the turn of the century strike me as pretty good candidates for such a plot.