Do you need antivirus software for Macs?

Question

Hi there,
I purchased a new iMac yesterday, and I was wondering if I need antivirus software for it?  Thanks!

Answer 1

There are two trains of thought here. Ultimately you'll need to decide which one fits you and your usage.
In general, there are no true viruses on Mac OS X - that is, no software that can just infect your machine and self-replicate without any user involvement.
However, that's not to say that malware doesn't exist. There are several known trojans on Mac OS X - software that's advertised to do one thing but actually doesn't something else (generally malicious) behind the scenes. These applications typically use some social-engineering or other guise to fool you into thinking they're legitimate - for example, you might visit a web site that pops up a message saying you need a certain software update in order to access the site, along with a link to 'conveniently' install that software, only to find it's installing something completely different.
The difference here is that trojan applications like this require some kind of user input and usually require you to authenticate your username and password in order to install. If you only install trusted software and are smart about knowing when you should/should not need to enter your password then you're pretty immune from such tricks. If there are multiple users on the machine (especially if they all have admin access), this problem becomes compounded since it only takes one person to let down their guard.
Then, there's the third class of malware in which your machine becomes a vehicle for viruses, even if you're not affected yourself. A classic example here is email and/or distributing software that gets opened on othe platforms. For example, if you recieve a document that's infected with a Windows virus, it can and will do nothing on your machine. However, if you then forward that document to other users, they may open it thinking it's trusted (it came from someone they know), only to find it infects their machine.
This kind of problem is more prevalent in mixed-platform corporate environments, and is exascerbated when you consider that things like Microsoft Word documents and PDF files have been carriers of this kind of malware in the past.
A good anti-virus application would detect and identify these kinds of malware, even though they cannot affect your machine itself.
So, do you need anti-virus? Probably not if you're careful and don't share much content with other users (especially other users on other platforms). However, there's generally little downside to doing so.