Originally posted by slightly
Although there are few Mac viruses now, it only takes a determined Machead with a penchant for trouble to come up with something.
You can compile an Applescript which will get addresses from Address Book and send mail to those addresses. The script can also deliver a nasty payload (eg wipe your hard drive). I don't have the flexibility to test this out on my system, but I believe, if the user is logged in as an admin (which, on most single-user setups, seems pretty likely), I don't think there's anything to stop Applescript doing this.
The key, of course, is to ensure that you're smarter than the computer. I'm not even sure if virus scanners will pick up attachments of the above type.
Panther will make security a little easier by making it simple to switch from an admin to a user with few privileges, but still and all, be careful out there.
Matt