For one of my digressive footnotes, I have been thinking about this question recently.
It would be beyond ordinary people, but if you had all the resources of the Chinese or Russian state at your disposal? It would not be easy. But there are some things that make it less hard.
For one, behind the scenes there is a lot of shared infrastructure in the polling industry. Different polling firms use the same telephone call centre operations. Different polling firms also use the same software. Different polling data is stored in the same cloud services.
There is no one call centre, one piece of software and one cloud to corrupt. You would need to corrupt multiple things, but not nearly as many as the number of polling firms may make it seem.
Could the Chinese bury a hidden back door in a shared piece of code used in multiple polling firms that provides hackers access which is then used to pollute final pre-election polls?
Of course, you would not need to hack every poll. Just enough to make the others look like weird outliers. Weird outliers which could also be discredited by a campaign of online disinformation, such as faked leaked documents over who really owns certain polling firms.
It is certainly plausible enough to make a Hollywood movie out of the idea. It is also one of the more niche reasons why being ‘99% certain’ or similar about what the polls says is unwise. There are an awful lot of very unlikely events – including sudden illness or war – that you have to pack into that remaining 1%. And 1% is super, massively unlikely. With a general election every four years typically, saying there is a 1% chance of something is pegging it at a 1 in 400 years chance. Four. Hundred. Years.
So don’t worry too much about the hacking risk. But do worry about those who tout 99% type statistics.