OK, look. Semantic debates aside, there are two general types of malware you need to wary of:
1. The kind that can sneak into your system without your knowledge, and without your intervention. This kind is dangerous because you don't know how it showed up, or what you might have done to get it there. This is the kind of virus that could infect your computer simply by having it turned on. The only way to detect this kind of virus is with a virus scanner that is continually, actively, checking your computer, and/or to block open ports or vulnerabilities that these viruses take advantage of (e.g. use a firewall).
2. The kind that you allowed into your computer, by opening an application, clicking on a link, installing a program, etc. On a Mac, you often have to type your password in to allow installation of any software that affects system services. If one of these shows up on your computer, it is guaranteed to be traced back to some action that YOU performed.
EVERY PLATFORM has variations of number 2. There is simply no way around that.However, on a Mac, they are extremely rare because, as the thread above indicates, the only places they have been seen "in the wild" are on porn sites and in pirated torrents. Avoid those two things, and exercise common sense when people send you attachments that seem fishy, and you're good to go. Even Facebook can be a vector for this sort of attack (if your friends are all suddenly joining groups with names like "YOU WON'T BELIEVE WHAT SHE DID WHEN SHE SAW THIS VIDEO!" -- don't click it. I bet it tries to install something that propagates itself further around Facebook.)
OS X has NO current instances of number 1. A continuous-scanning virus checker is not necessary unless you think there is a chance you will be tricked into allowing a trojan/worm/malware (number 2) into your computer. But again, with common sense and vigilance, you should be just fine.
1. The kind that can sneak into your system without your knowledge, and without your intervention. This kind is dangerous because you don't know how it showed up, or what you might have done to get it there. This is the kind of virus that could infect your computer simply by having it turned on. The only way to detect this kind of virus is with a virus scanner that is continually, actively, checking your computer, and/or to block open ports or vulnerabilities that these viruses take advantage of (e.g. use a firewall).
2. The kind that you allowed into your computer, by opening an application, clicking on a link, installing a program, etc. On a Mac, you often have to type your password in to allow installation of any software that affects system services. If one of these shows up on your computer, it is guaranteed to be traced back to some action that YOU performed.
EVERY PLATFORM has variations of number 2. There is simply no way around that.However, on a Mac, they are extremely rare because, as the thread above indicates, the only places they have been seen "in the wild" are on porn sites and in pirated torrents. Avoid those two things, and exercise common sense when people send you attachments that seem fishy, and you're good to go. Even Facebook can be a vector for this sort of attack (if your friends are all suddenly joining groups with names like "YOU WON'T BELIEVE WHAT SHE DID WHEN SHE SAW THIS VIDEO!" -- don't click it. I bet it tries to install something that propagates itself further around Facebook.)
OS X has NO current instances of number 1. A continuous-scanning virus checker is not necessary unless you think there is a chance you will be tricked into allowing a trojan/worm/malware (number 2) into your computer. But again, with common sense and vigilance, you should be just fine.