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I recently got a Mac, and am transferring files from my old Windows laptop which had kept freezing with very high hard-drive activity, and may or may not be infected with malware. I'm wondering if there's a chance of my Mac being infected by malware from photos, documents, videos and music transferred from a Windows machine?

If so, which antivirus would you recommend me to get on my Mac? Are Sophos and Avira any good?

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up vote 6 down vote accepted

The short answer is "No, your Mac should not get infected".

The a bit longer answer is "it depends". You should be fine with photos, videos and music, but there might a very small risk with documents (depending on the format) and anything html-related (which might access a malware server or something). But given the current state of malware on OS X I wouldn't worry too much.

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While your Mac won't show any symptoms of infection by Windows malware, it can carry and pass Windows viruses on to other computers or networks. Think of your Mac like a Typhoid Mary if it is housing any Windows malware.

Your Mac can get infected with Mac malware, which is a growing threat these days.

I would't bother putting any Windows antivirus software on your Mac. I recommend Intego, an Apple antivirus company that focuses on protecting Macs. You can check them out here:

Hope this help!

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Do you have sources/references which show that malware on OS X is a growing threat? – patrix Feb 15 '13 at 19:10
Fine, but where exactly? Without some clear source it seems to be rather speculations based on rumors. – patrix Feb 15 '13 at 20:46
It's a trend I noticed being reported on more often. Here are some sources: May 18, 2011:… September 27, 2011:… June 6, 2012:… October 8, 2012:… – Martin Feb 15 '13 at 20:50
→ martin: could you add ClamXav I'm using it at a professionnal level on a set of thousands Mac (10.5 → 10.8), with positive and correct results. – daniel Azuelos May 10 '13 at 8:36
→ martin: Typhoid Mary = excellent allegory! – daniel Azuelos May 10 '13 at 8:41

It won't affect your Mac. But it may infect other Windows systems that your Mac comes in contact with.

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Actually, there is indeed a low but very real chance to get infected.

There are 2 ways in which files on a disk can infect a computer:

  1. If the file is an executable e.g. .exe or .app, it contains code that is run on the machine if a user tells the computer to do so. Windows executables cannot run on a Mac and Mac executables cannot run on Windows, so a Windows executable cannot infect a Mac. Infected Windows executables are harmless on a Mac, and infected Mac executables are harmless on a Windows machine.

  2. If the file has to be opened by a host program e.g. Adobe Acrobat, or Flash Player, the file can use flaws in the host program to make the host program install and execute a virus. The same is the case for java files, several text document formats, some image formats, etc. It's possible that a Windows machine contains such files on a harddisk which can attack a Mac, as soon as the Mac user decides to open these files. See this question on security.stackexchange.

In any case, if you manage to infect the Mac with a Windows harddisk, or the other way around, the actual malware will be different. The same exploit will almost certainly never work on both Windows and Macs.

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An experimental (very rare) kernel infection exists for the Mac, called Thunderstrike.

It is actually still being developed as a proof of concept, along with some other experimental malware for OS X, but at its current stage (version 2) it is able to travel via thunderbolt storage devices and infect other Macs.

Some conspire that the NSA is behind many of the kernel vulnerabilities present in the OS X kernel, but that's just thoughts and speculations derived from (possibly) false rumours.

Anyway, I'll throw a few links and sources below and you can read some more 'in-depth' stuff if you're willing to.

Don't worry, you're safe if you don't click on unknown links :)

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