This week we heard of two virus-attacks against Macs, out in the wild. But wait… Is that really possible? I thought Macs were immune to viruses!

Sorry folks, they’re not. Never were. The problem is that a lot of people don’t seem to really understand what viruses are, and what makes a computer vulnerable to them.

Basically, a virus is a program written by a person (they don’t just grow by themselves), for the purpose of attacking specific types of machines. Remember the Stuxnet virus that made the news in July 2010? That was designed to attack a specific Siemens industrial process control system, which was being used by Iran in their efforts to create nuclear weapons. That’s how specific viruses can be.

So why haven’t we seem them very often on Macs? My thought is that there are two primary reasons:

1. Thusfar, the Mac platform has simply not been considered worth attacking because of Apple’s relative marketshare to Windows. Although recently, Apple has had tremendous increases in marketshare, there are still many more Windows machines than Macs out there. If you were going to write a virus to, say, steal credit card numbers from consumers, would you rather spend your efforts on systems with more users, or with relatively fewer users? More PCs (and frankly, more less-educated users) means more targets, and that means more compromised machines. (There are even fewer viruses out there that attack Linux systems, for the same reason.)
2. Windows XP and earlier had a lot of security vulnerabilities. A lot more than Vista and Windows 7. So the operating systems were easier to exploit. And the vast majority of Windows machines still out there (at least as of this article) run Windows XP.

Given those two reasons: More opportunity, and easier to break – it makes sense that most viruses were written to attack Windows systems. But as Apple systems gain more market traction, they become much more attractive to malware writers. The fact that Mac users are not used to using anti-virus software can potentially make it worse. And the fact that Mac users have never had to worry about dirty social-engineering tricks that Windows users have had for years – like the ones used by the most recent attacks – can potentially cause this to become very bad, very quickly.

So Mac users – don’t be so confident that you don’t need antivirus software, and start being vigilant about where you go, and what you allow to install on your machines. This is only going to increase.