Now I am thoroughly confused as to whether I need AV protection or not. Can anyone simplify this for a simple minded person like me.
Among Macintosh users the term "malware" is used to describe any sort of malicious software. So Worms, Trojan Horses, Viruses, etc. are all malware.
Macintosh users refer to "viruses" to mean self-replicating malware. That is, malware that doesn't require user intervention to spread.
To complicate things, many Windows users use the term "virus" to refer to *all malware*, no matter what the type. Though the correct technical definition of "virus", even in the Windows world, is the more narrow definition that Mac users use. See:
https://en.wikipedia.org/wiki/Computer_virus
Now, there *is* malware (though a very limited amount) for the Macintosh. Here's a list of all known malware for the Macintosh, save for a couple of more recent examples:
http://www.thesafemac.com/mmg-catalog/
About half of what is in that list is now extinct in that it does not exist in the wild. The other half tend to be extremely rare, and/or are not a concern because updates to OS X, or to Java, or to Flash, have provided some degree of inoculation against them. (You can still get them if you haven't updated your software, or if you have turned off certain protections, or if you are running a very old version of the MacOS, etc. But even then, since all of this malware is rare, you still aren't likely to become infected.)
There are only two pieces of software in the list I cited above that could be technically defined as "viruses" in that they are self replicating. None of these currently exist in the wild. (I'm not sure that either ever did.) So, anyone who says that there are "no viruses for the Macintosh" is technically correct if they are speaking about self-replicating malware existing in the wild (an admittedly narrow definition), but incorrect if they really mean that "there is no malware for the Macintosh."
There *is* malware for the Macintosh. However, at the present time, there is so little risk posed by Mac malware that the vast majority of Macintosh users don't run third-party anti-virus software. Despite this you just about never hear a believable report of any Mac users becoming infected.
Of course, there is already anti-virus software built-in to the MacOS:
XProtect/File Quarantine/Gatekeeper
http://en.wikipedia.org/wiki/Xprotect
https://support.apple.com/en-us/HT201940
http://www.macworld.com/article/1165408/mountain_lion_hands_on_with_gatekeeper.html
http://www.thesafemac.com/mmg-builtin/
... and Apple has been quite good at automatically updating this software are new malware threats arise. In fact, Apple often updates your OS to inoculate you against malware threats even before you might hear about any new such threat.
Now, couple this with the fact that just about all of the fully interactive third-party Macintosh anti-virus programs have been known to cause severe slowdowns, and sometimes nasty software conflicts. This gets you to the common guidance that "anti-virus software for the Macintosh is often more trouble than it's worth." Nothing about this has changed. There are no recent threats to the Mac that are so pervasive or so extremely virulent or which have not been blocked by Apple themselves, that would require you to risk the performance and stability of your Macintosh to avoid them by installing anti-virus software.
The list of malware that I referenced above has, what?, about 50 examples? This is a different universe than what you will find for Windows. There are literally well over a MILLION examples of malware for Windows. In fact, the number surpassed a million NINE YEARS AGO:
http://news.bbc.co.uk/2/hi/technology/7340315.stm
If you follow Windows-oriented publications or news sites, you will see that there are new, seriously malicious threats introduced practically on a daily basis for Windows.
My best advice is to not get your Macintosh advice from a Windows user or from the popular press. Totally ignore anything they say about the Macintosh, even if they are nationally, or internationally syndicated. Get your Mac advice from Macintosh news sites and related resources.
As a postscript, "adware" isn't at all malicious, it's simply very annoying. So it is not technically considered "malware" in the industry. MalwareBytes is excellent for finding and eradicating adware. As it is free, and not fully interactive (so it won't cause slowdowns or software conflicts), there is no downside in using it for that. However, no matter what it says on their Web site, MalwareBytes is not a comprehensive anti-maiware solution. If you don't believe me, you can prove it to yourself by running any good commercial anti-virus program. See how long it takes to do a scan. Then run MalwareBytes and see how long it takes to do a scan. (Spoiler alert: you can't comprehensively look for and deal with malware in about 20 seconds. Good anti-virus software usually takes hours to do a scan.)
I hope this makes things clearer.
