The prefix code seems like a good idea, but it's only one digit longer than the security code to get into my phone. Hardly seems like the most secure method to prevent hacking. At least they gave starship computer security some thought, though....
This movie was made in the early 80's so dated security measures can be forgiven. At the time that seemed like a highly advanced security precaution. Really the only thing that surprised me is, what's the point of having these security prefix codes if any ship can look them up?