OS9 was sort of a toy, because it did not have the multitasking features required of a modern OS. but secure? you betcha!
i m not saying that it wasn t chock full of holes, because who knows? the answer is noone! crackers don t waste their time looking for holes in OS9, because there weren t enough users. and the lack of a command line makes it hard (read: almost impossible) to run scripts remotely. to attack the services, you would have to do real coding. it had some real bonehead problems, and if you found one, you could easily crash it, but they were really hard to find.
i have heard that even the OS had become badly undocumented by the apple developers, because of years of using very limited ranges of hardware, and reusing ancient code.
there was a mac company that used to put up a mac server on the internet, and give out the IP address, and offer $10,000 to the cracker who gained access, and edited a web page, and for the first couple of years, no one got it! i think the third year, they added a bunch of third party software, and someone found a hole in one of those third party servers, and gained access.
based on this result, the army decided to migrate a large portion of its sensitive servers to OS9. so it is totally believable that the FBI might try it.
nota bene! i am not claiming that OS9 was air tight. on the contrary, i will bet that OS9 was swiss cheese in terms of security. but the point is that it is not well documented, and has no command line, and is just not seen much as a server platform. apple uses a lot of closed up proprietary technologies, and crackers just didn t pay attention to it. compare that with windows, which has ever cracker bucking for it, and its more than willing to run vbs sccripts, and .bat files (true, i suppose you could try applescript on OS9). and of course, for performance, it was terrible. if you accidentally click on a menu, and leave it open, the server just stops. pretty terrible, eh?