[general_re]

The damage to the system will then be the infection or deletion of the user's files, period. That is all they could manage with a virus (an actual locally executed file) on a Mac.

"Enter your administrator password to update your system!"

And some fraction of users will do it. I know it, you know it, we all know it ;)

[antiRepublicrat]

"Enter your administrator password to update your system!"

Most people on Macs will be running as Administrator, but that's not the same thing as it is on Windows. Those more advanced users who want to mess with Windows-like admin privileges ("root") that can actually screw the system first must set up access to root, which is by default disabled. Those advanced users are less likely to fall for stupid tricks. It's possible it could still happen, but a trojan built to trash OS X installations would have very few successes.

[HAL9000]

"Enter your administrator password to update your system!" And some fraction of users will do it. I know it, you know it, we all know it ;)

Yes, but those same users have probably forgotten their administrator password anyway.

Meanwhile, my neighbor called last night and told me that his Windows computer was destroyed by a real virus. He lost all of his files.