[null and void]

Not hackable. Period.

Really?

It's impossible to update the software once the thing ships?

There's no provision for maintenance and repair?

Granted, that would require a whole 'nother level of attack, not an outsider hacking in, but sabotage from within.

But I would argue that the religion of al taqiyya is quite capable of placing an agent anywhere.

[Tzfat]

It's impossible to update the software once the thing ships?

Some of it. What you are referring to is firmware type software though, and is normally only revised with new hardware.

For nav databases etc., it has a special data port. The built-in checksum makes sure it is from the manufacturer and is valid.