Exactly, you can get away with safe computing alone if you use the computer in isolation, don't trade data, don't connect to varying networks, don't have significant email/attachments, don't require third party software and or plugins, browse only known sites, disable some functionality, etc.
In the real world frequently the opposite very much applies, try telling a SysAdmin that your computer is safe to connect to their network, you don't need AV because you practise safe computing the answer is obvious, you wont be granted access.
"Mac users can often be heard to say I dont need antivirus software, I have an Apple. Unfortunately, this is a misguided conclusion. Whilst the dangers are certainly much less than with Windows computers, they do exist nonetheless. If nothing else, the recent spread of Mac Trojans proves this. Mac users who think they do not need to concern themselves have created an illusion."
Malware for OS X is on the rise and will continue to do, as the platform gains further momentum. People with Mac`s without a software security solution in reality have no idea what they are potentially retaining or passing on their unprotected systems be it OS X or Windows orientated malware, equally they will be adamant that their system are 100% clean, yet they have no way to verify, this all this adds up to one thing "assumption".
Best approach to security is a "fluid" one, adapting to the malware environment versus one`s own/families workflow. Ultimately I know some will never change, however others may visit and see it`s not a one-sided discussion and consider their security requirements versus their own workflow`s, and not blindly follow "Mac`s don't need AntiVirus"
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