It does raise the question, how difficult is it to reprogram a voting machine?
That is a topic which has been examined in detail by many researchers, litigants, activists, vendors, commissions, and other parties. Some voting machines turned out to be poorly designed and capable of being reprogrammed with malicious code. Others, due to their design, would be much harder to attack, unless the attacker had undetected access to the machines.
Unfortunately, the worthwhile efforts to secure voting machines are getting mixed up with accusations made by the Stein campaign that are in tinfoil hat territory.
Some of the machines Stein contends could have been hacked by "Russians" or some other nefarious group, would require the hackers to have physical access to the machines in order to implement the software changes. It really stretches the imagination to think that either a group of ninja technicians broke into the voting machine warehouses and altered hundreds or thousands of machines (and perfectly replaced the security seals), or that the Democrat election officials in Pennsylvania were actually participating in some wild conspiracy to elect the Republican candidate.
When confronted with the actual circumstances Stein's experts fall back on complex conspiracy claims. You see, even though independent and party observers test a random sample of machines, how do you know that the election officials didn't remove the hacked code from those machines so they would pass the test? They had time between when they were given the numbers of the machines to be tested and when the tests were run! So they could have covered up the hacking.
The theories they are advancing are past speculative and into tinfoil hat territory. Where are Scully and Muldaur when you need them.