The existence of whole industrial and home computer industry kinda proves that the models were effective and worked. Yes, there were vulnerabilities and viruses but that did not stop the computer industry from growing and proving its worth.
This is true, but "worked" does mean it was secure by whatever we standard we consider good today.
That might be because we (at least on sites like this) are being overzealous about security. Or it might mean that in the modern environment, security is more of the concerns than in the halcyon days of MS-DOS.
