That's because the researcher didn't do that on an actual plane. In fact it wasn't even a simulator, it was a virtualized simulator where he put the systems all on the same bus. On top of that the guy was only able to listen in on traffic.
Just the existence of such a device gives me reasonable cause to believe that there's more interconnection than "isolated just fine". While I have a lot of respect for the engineering processes that go into aviation systems, I've also had enough practical experience in IT security to know that blind faith in things being done right is foolish.
[edit] I've seen the claim made more than once in this thread without a source. I understand that the article was probably very wrong. I'm just interested to know if a reputable publication has confirmed this or if it's just conjecture.
I know this doesn't mean diddly squat, but my sister worked for a manufacturer of airline wiring harnesses up until very recently, and when I asked about it, she mentioned that they were not interconnected or exposed to one another. I don't believe they did the really huge jets, but regional and private sized jet harnesses instead, so it could be different in that aspect also.
Can you provide a reputable source to prove that President Obama is not a disguised lizard alien? ☺ I mean the original article was so obviously nonsense on the face of it that no refutation should be necessary.
The entire story is bogus.
The systems are isolated just fine.