Apple Macs Could Be Spreading Windows Malware

Dennis Faas's picture

Prominent security firm Sophos has discovered that approximately one out of every five Mac computers is infected with Windows malware. And while such infections pose little threat to the Macs themselves, they could spread to Windows computers.

The report is the result of Sophos' work in analyzing the contents of about 100,000 Apple Macintosh computers, using the company's own anti-virus software for the Mac world. The analysis shows that 20 per cent of the computers are carrying some kind of Windows-oriented malware.

About 2.7 per cent of the Mac computers, or about one in thirty-seven of the machines, were infected with malware capable of becoming active within Apple's own OS X environment.

Infections Communicable by USB Drive, Email, or Download

To many observers, Sophos' findings seem unremarkable. After all, Windows malware can't have a significant impact on the performance of a Mac. But Sophos analyst Graham Cluley says that Mac and Windows users should both be concerned about this level of infection.

"Although Windows malware on Macs won't cause symptoms (unless users also run Windows on their computers), it can still be spread to others," Cluley noted in a recent blog post. (Source:

In fact, Cluley likened this kind of malware to a communicable disease in animals or humans: it doesn't necessarily affect the host organism, but it can prove harmful to many others who merely come into contact with the infected host and thereby receive the infection.

As an example, Cluley cited the disease Chlamydia. "Just like malware on your computer, Chlamydia commonly shows no obvious symptoms. But left undetected Chlamydia can caused serious problems, such as infertility," Cluley noted. (Source:

Cluley went on to suggest that Windows-oriented malware found on Macs could spread to Windows-based machines via USB drives, email attachments, or website downloads.

Flashback, DNSChanger Malware Found

Besides the threat an infected Mac may poses to one's friends and colleagues whose computers run Windows, Mac users should also be concerned about Sophos' finding that some 2,700 of the Macintosh computers tested had infections that could directly cause them harm.

Sophos says that several of the infections discovered are of a serious nature. They include Flashback, which logs keystrokes, investigates data files, and monitors web activity in efforts to steal usernames and passwords.

Another of the Mac infections Sophos found involves DNSChanger, which causes a computer to connect with fraudulent Internet servers and subsequently visit phony websites instead of those the user actually desires. (Source:

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