Apparently this is a hard question. Let me provide an answer. If we're talking about 'hackers' in the computer-centric sense, as the article seems to be, yes, you can. Here are several examples of cars completely immune to computer hackers:
Ford Mustang, 1968
Dodge Charger R/T, 1970
Hot Rod Lincoln
By virtue of which, see here and here, and also below:
You know what else is hacker-proof? My motorcycles. Not a computer on the things anywhere.
So yeah, it can be done. The results look pretty good from where I sit.