I always suggest: Just because you don't use Windows it doesn't mean, you don't have to bother about antivirus software, firewall and system upgrades! Every code, even written under Steve Jobs, is somewhere buggy, every developer will forget about a security issue, and it just a matter of time until someone who is interested in demolishing a system will find it out.
When you care about your system, actually every OS is secured. I just believe, that MacOS is in the moment, the one that you have to care at least about. But that never means, you don't have to at all!

I read an article once (sorry, don't have the link) where it suggested there have only ever been 2 viruses in macs, and in each case the virus was harmless. Apparently there's no such thing as a mac virus at present.

I've had my mac for a good few months now - I browse torrent sites etc on a daily basis with NO firewall/antivirus whatsoever, I so far don't seem to have found a virus. Some would suggest it would be more harmful to install unneeded antivirus software.

Yes, recently Kaspersky announced anti virus for mac users. http://www.beepthegeek.com/2009/11/hi-mac-users-now-get-advanced-internet-protection.html

I protect my mac with Protemac netMine

There no viruses in macos because on the simple fact that like in a human body a virus needs the right conditions to prosper. Macos does not provide theses conditions as any unix system out there.

On the subject of rumor they have been only viruses by fantasy and viruses in theory but no real threat.

Do not install antivirus programs on your mac, as they can make the os unstable. Mots of these antivirus programms are made by windows developers with limited knowledge of macos that only care to make profit.

Its most unlikely that a virus that will be a substantial threat will ever exist in macos. Apple is likely to hunt down the hacker that will make it and make him pay literally.

The age of viruses actually has passed long time ago, they were succeeded by worms and trojan horses but even those are becoming an extinct race. The future is spyware as companies make money on it by stealing your personally information without leaving a trace. In that kind of threat macos is stronger but still has room of improvement.

Unfortunately for these kind of threat even a firewall is not enough.

So in short , stop worrying and start surfying freely, you are most likely being hit by a comet than a virus penetration your macos.

I definitely have to contradict you! There's nothing that I hate more than giving people wrong advice, especially if these kind of person don't seem to have a single clue what they are talking about! And on top of that: Why not protecting if it's so simple as today?

@all: Always, but really always protect your computer! Don't discuss whether you have Windows, Mac, Linux, ChromeOS or any system that comes up in the future running. Every Operating System does have vulnerabilities in the source-code. And every operating system can be attacked by hackers and viruses.

Also remember: even the best antivirus-software doesn't give you an absolute protection. Always be careful what programmes you install and who you let work with your computer. So the best thing is to keep these 4 guidelines in mind:

1. Always create TWO accounts! First one as administrator (or root under Linux) with a very strong password and DON'T use it. This account is just for changing the preferences of the system. And try not to be online while using it.
The second one is your normal account that you use for office, web and whatever you do. In 1 out of 50 days you don't even have to login with the administrator password.

2. Activate the firewall and install a virus-software! Maybe your computer will never be attacked by hackers because they can't modify your system as you work with your second account. But maybe a bug in the kernel will be found and someone is interested in the docs you have, to use your computer for hacking or just want to harm you because they find it funny. And a recent surveillance found out that bugs aren't fixed by apple as fast as one might want you.

3. Be skeptical when installing software! Think twice if you really trust that person who wrote the stuff. In general you can't do anything wrong if you stick to point 1 and 2 but that software can still slow down the computer or internet-connection. Of you are unsure check the apple-website and see, if it's listed there under downloads or any computer-magazine that you trust. I don't wanna cause any panic: More than 99% of the software that's out there is great, but you can always get one of the ones that really harms your computer.

4. Don't give your password away: When installing or removing programmes from your application-folder, changing the system-preferences or running a script you have to enter your password. Thats fine. But as soon as you enter your password in a window that looks different to the MacOS standard one, be very critical. Once given the password to the programme it could use it to harm your system. Doublecheck the programme in the Internet and find out if that programme really needs it.

These 4 points aren't hard to follow. The second account is done in about 10 minutes, the virus-software as well. All the other points are just to keep in mind. Noone has to be in panic just because he/she protects the computer. It's just better to be carefully than having to reinstall the system one day and be annoyed that all data are lost.

There are many documents about security under macos out the in the net. Just google around and look for websites that you trust.