Macworld — When you say "computer security," most people think "viruses," "worms," and other forms of malware. They also think, "Mac users don't have to worry about it." And they're correct. But that could always change. So it pays to keep your eyes open for credible reports of new Mac security problems and to change your computing habits accordingly.

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Viruses and worms

Let's be completely clear: there are absolutely no technical barriers preventing worms or viruses from infecting the Mac platform. A cursory review of Apple's own security updates will reveal a long list of vulnerabilities that a knowledgeable attacker could easily exploit in a Mac virus or worm. Some of these flaws have been public for weeks or months before Apple released fixes for them.

But despite the opportunities, we have yet to see any widespread malware for Macs; your risk of infection is essentially zero.

The extremely low incidence of Mac-specific malware is a source of continual debate in the security community. It might be due to Apple's still relatively low market share. It might be because malware authors have years of experience exploiting PCs. I think it's probably a combination of factors.

Whatever the reason, it's frustrating for Mac security vendors, who see the potential for widespread attacks, but never the execution. And until those attacks appear, there's little reason for the average Apple user to invest in antivirus software.

The major exceptions: If you're a corporate user on a network with Windows users, or you regularly download software from risky parts of the Internet. And I would advise you to use an e-mail service that filters for viruses, since e-mail is the most common vector of attack. All major services, including MobileMe, Google Mail, Hotmail, and Yahoo (YHOO), filter for malware, as do many Internet service providers.

Botnets

The terms virus, worm, and Trojan horse differentiate malware based on how it infects your computer. The term botnet refers to what the software does once you're compromised.

A botnet is a collection of infected computers tied together and controlled by the attacker. Bad guys use these to send spam, distribute other malware, launch anonymous attacks over the Net, or coordinate large, distributed denial of service attacks (in which thousands of computers hit a single site at once to overwhelm its bandwidth).

In the past year, we saw one small botnet built from Macs, which had been compromised by a trojan hidden in illegally downloaded software. But since your Mac first needs to be infected some form of malware before it can be made part of a botnet, the chances that it'll end up in a herd are still extremely low.

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