Typhoid Mary

Originally published  Tuesday, February 17, 2009

There is this idea floating around out there that Macintoshes are a prime vector for spreading Windows viruses to unsuspecting Windows users. We Mac users, who so smugly like to remind Windows users that we don’t run anti-virus software because there are currently exactly zero viruses (and very few Trojans or worms or other malware) that infect Mac OS X, are latter-day Typhoid Marys, unwittingly spreading viruses that don’t infect us to the beleaguered Windows users who wisely employ as much protection against viruses and other malware as they can muster.

Nothing could be further from the truth. The reality is that it is extremely unlikely that a virus will be spread from a Macintosh to a Windows computer, unless, of course it comes from the Windows partition of an Intel Mac on which the user is running Windows. And any Mac users who accesses the Internet on their Windows partition had better be running anti-virus software, or their Windows partition will soon be infected by Windows viruses.

But shouldn’t Mac users run anti-virus software simply out of consideration for their Windows-using friends? In a word, No. Here’s why.

First of all, it is not the responsibility of Mac users to protect Windows users from Windows viruses. It is the responsibility of Windows users to protect themselves from the malware that plagues Windows. I know that sounds harsh and uncaring, but it’s undeniable that only a fool or a naïf would go online with Windows without protection.

It’s not that Mac users are unsympathetic. We certainly wouldn’t want to pass viruses on to our friends, even inadvertently. And some well-meaning but ill-informed Mac users actually run anti-virus software on their Macs for just this reason. But just think it through. Say that I got an e-mail that had a Windows virus attached.  Since a Windows program cannot be executed by Mac OS X, and a virus has to be executed in order to spread itself, the virus has reached a dead end when it lands on my computer. It cannot get into my address book and send copies of itself to every address like it would on a PC.

The only way I could pass it on to anyone would be to forward that particular e-mail along with the malicious attachment. Chances are good that I would have no reason to forward the message to anyone. I would probably recognize that the e-mail contained a virus and just delete it.

Of course, there is a slim chance that I might pass the virus-containing e-mail along to some unsuspecting Windows user. So shouldn’t I be running a program to detect Windows viruses just in case? Well, no. Why not? you may ask. I’ll explain.

Let’s say that I receive an e-mail that has a Windows virus attached. The virus won’t infect my Mac, but let’s say that I forward the e-mail to a Windows user complete with the attachment. One of two things will happen. Either the Windows-using recipient’s anti-virus program will detect the virus attached to the e-mail, or it won’t. If it does detect it, then no harm was done. If it doesn’t detect it, then it isn’t logical to think that any anti-virus program I might run on my Mac would have detected the virus, either.

Windows users have nothing to fear from us Mac users. We won’t be spreading viruses to their precious PCs.

Now back to our regularly scheduled program. ☺



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