Malware on Macs

Rory Bowman at

Q: I think I may have a virus on my Mac? Can you come remove it?

A:Every two or three weeks I get a phone call from a stranger who is convinced they have a virus on their Macintosh or a client who wants to know if they shouldn’t get some sort of anti-virus program, and every six months or so I see a brief flurry of breathless Internet postings about how there is a report of some new and hitherto-unseen Macintosh “virus,” often with a smirk as if to say finally the smug macolytes have gotten their come-uppance. Despite these things I almost never encourage people to get anti-virus programs such as Norton, because the Macintosh is simply not as prone to malware of various kinds as Windows is.

“Malware” is a general term for computer software designed to do harm to its host computer, be it a spyware, a worm, a trojan horse or a virus. For various technical reasons having to do with security design, it has ALWAYS been much simpler to write malware for DOS and Windows than for Macintosh or Unix, including Linux. Whenever there has been an opportunity for Microsoft to choose its own convenience over security, they have done so, which is one of the reasons lots of IT people prefer it: various maintenance tasks and automation are simpler for the good guys. Unfortunately, the same tools the good guys use are also available to the bad guys, and this general lapse encourages a lot of bad programming decisions.

If you have a Macintosh you are not invulnerable to malware, there is just a lot less of it. In over twenty years of working on the Macintosh myself I have seen a total of six viral “infections” on my own machines, none of which would run on Mac OS 9 or X and three of which were from a gradeschool student who reinfected me with the same floppy in quick succession. Among my clients over the past eight years, I have seen scores (even hundreds) of Windows viruses, but only four of which affected the Mac. Just as I am not going to get pregnant as a man and you (as a human) are not going to get feline leukemia, Windows viruses are not going to hurt your Macintosh, although you might unwittingly give them to a Windows user by including them on a CD or forwarding them within a Microsoft Office Word or Excel macro.

The way you are most likely to expose yourself to malware as a Macintosh user is through a “trojan horse” attack: downloading something you think is a program to do one thing and finding out it does something else. This is most likely to happen through “file-sharing” software such as LimeWire and similar shady areas of the Internet. Just as you shouldn’t eat or drink everything handed to you at a party, you shouldn’t assume that because you are on a Macintosh you are invulnerable to malware. Observe the basic cautions of not opening attachments from strangers, not passing along files you do not understand or isntalling software of unknown provenance.

For folks who operate Macs within mixed networks with Windows users, an anti-virus program makes sense, as a courtesy, but is not yet necessary. Below are a few links of interest to observe how a trojan-horse program works, and to learn more about malware generally.

If you are running Safari on OS X, go into your preferences now and in the “General” pane uncheck the option which automatically opens “safe” files. This is the vulnerability the Yahoo article describes, and the most serious OS X has yet seen.

You can download the free open-source Clam AV anti-virus program at

An excellent critique of the original AP story may be found at

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1 Response to Malware on Macs

  1. Rory Bowman says:

    An older article on the Leap-A “Virus” (really a trojan)
    A more recent article with general tips

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