Macintosh

As there are fewer Macs out there than Windows machines, virus writers tend to not write viruses for Macs. They go for numbers. On top of that the Mac OS makes it somewhat more difficult to get a good virus going. There are some, but very few. The result is you can ignore antivirus and in all likelihood never have a problem. But if you want to be really sure, you can still get it.

It never hurts to have anti-virus software, having said that, if you pay attention to what you are downloading you should have less issues with virus's and the likes on your Mac.

"Brain" is the best AV, available for Mac, Linux und Windows.

Nothing can stop "flyby" infections like the Java Exploid for OSX Lion in the early 2012.

Keep your Mind and Eyes open and you can surf the web probably Virus free (at least with OSX and Linux)

Windows Malware/Viruses: Ninjas in the night come in through your many open windows, and steal everything without you knowing. They also kill your cat.



Mac Malware/Viruses: A man knocks on your door asking for a copy of your house keys, asking when you won't be home today, and if you wouldn't mind him being over. He assures you he is a good person.

My advice is, if you don't have a router between your computer and your ISP, get one. That will take care of the basic bots that spam IP addresses looking for responsive computers.
After that, well it's not just that Windows is on many more machines (as many of those are office drone boxes with nothing on them but Outlook, Excel and Powerpoint). It's also that parts of Windows, in particular Explorer and the media player, have been chock full of bad security design for years. Improvements have been made recently, but Windows has long been an easier target overall.

I can tell you that I've been running for years with no AV software on my Mac, just a router upstream. Periodically I download a scanner and look at my drive, I've never found anything more offensive than a couple tracking cookies, even though I download random crap pretty regularly.

That said, current malware is relying less and less on coding exploits, and more on social engineering. My favorite being the website that contains say, R-rated video of some B-list celebrity. You click on the webpage, and it tells you that you're missing a necessary codec for playback. you download it, it installs, and you get to watch your naughty videos. The website itself is exactly as promised... but that codec that you downloaded and gave permission to install is the virus. No hacks needed, the eager user cheerfully told it to install. Kinda hard for AV software to defend people from themselves.

P.P. MacKeeper is utter garbage. Don't go there.

I've been running Macs since 1995, with no machines suffering from Malware. The machines I use at the office have Symantec AV installed, and in the last three months I've had to reboot the system twice due to the AV system stalling while I was trying to log in. So in my case, having AV installed on a Mac only reduces the security and reliability of the system.

As for filtering viruses so you don't pass them along to your Windows using friends: first, I don't participate in "forward this to 10 friends in three minutes or you will die" chain spam, so between me not blindly following the directions in spam mail, and only forwarding attachments on that I know are safe, my Windows using friends have nothing to fear.

All/most of the existing malware for Mac OS X takes the form of Trojans: software that you must install in order for the malware to work. Thankfully Apple has removed Java and Flash from default installs of Mac OS X, so you don't have to worry about those two vulnerabilities any longer.

I prefer to avoid AV software simply because when the AV software breaks there is a significant risk of breaking the installed OS.

No, you do not need an Anti-Virus program on a Mac.

What you do need is the same as on every platform: Caution.
- Reduce infection vectors: Disable Java in your browser if you don't need it. (Apple did that by default after the FlashBack wave earlier this year.) Disable Flash for pages you don't need. (NoScript Plugin in Firefox can be used to whitelist pages like Youtube that require it). Same with JavaScript if you want to be really paranoid :)
- Don't download Software from untrusted sources. OS X Lion/Mountain Lion come with GateKeeper, which can help with that part a bit. But of course it's not perfect. Many developers don't yet bother to sign their software. (EVE Online for example is not signed)
- Don't run services you don't need. A router with NAT and Firewall can be useful if you want to provide local services.
- And most important: Keep your software up-to-date. This is very important for Programs that deal with the evil outside, such as web browsers or web browser plugins.

OS X has a simple signature based virus scanner built in, but it has no user interface and does not need to be enabled. It is probably mostly useless because it only detects old viruses (like any virus scanner), for which the infection vectors have already been closed.

There aren't as many Mac viruses as windows but they are still out there. Same rules apply, don't open strange email attachments. Be skeptical whenever a program asks for admin access. Stuff like that. But as far as needing an anti-virus, no I don't think you need it as much as windows users do so long as you are careful. But be warned, the more popular Macs become the more likely viruses will be released for them and Macs have been getting more popular the last few years so don't let your guard down.