Viruses, worms, trojans, spyware, and malware are written for a specific OS. Unlike Windows, Unix has always had a very strong security model of closing all ports, making use of a permission system, and is very strict on System wide modification.
Take for example:
If a Mac were a person, and it just met someone, it would invite that person over sometime, keep them under constant surveillance.
If a Windows box were a person, and it just met someone, it would give them its social security number, id, house and car keys, then leave that person alone in its house.
Think of it this way, you can't jam a SNES cartridge into a Playstation. Can malware be made for the Mac? Yes, but it won't work well or at all. For it to work it would have to require system administration access, that means you would actually have to approve the software's modifications.
If you double click something entitled "nakedpic0001.jpg" and it all of a sudden pops up with a request for administrator access, that is a red flag to anyone with common sense.
Windows fans have been claiming for years and years saying as Mac OS X became more popular a virus would show up. Its now 5 years later, 8 contests done and failed, and not a single virus for the Mac yet.
* This post has been modified
: 18 years ago