There was a time when being a “Mac person” meant being somewhat shielded from the usual onslaught of malicious software viruses and trojans lurking online. In fact, viruses targeting Mac computers were so rare that users probably became a bit too overconfident and boastful about the robustness of the platform.

But in 2009, the days of the carefree Mac user never giving a second thought to online security are long gone. Viruses, spyware, Trojans and other malware aimed at the Mac OSX operating system are becoming more common these days. For example, the dreaded Botnet trojan has now been ported over to attack Mac operating systems and steal sensitive information from users.

And while no one would deny that Windows PCs still have the greatest number of threats from online malware, according to recent research from Symantic, Mac viruses and trojans are becoming more prevalent, especially among users of peer-to-peer sharing sites. The company recently discovered two different versions of the Botnet trojan hiding inside pirated software for Mac OSX. Specifically, Adobe Photoshop for Mac, and Apple’s very own productivity software, iWork 09.

The cracked software provides an easy way for hackers to infiltrate a user’s computer — even a Mac. By downloading and installing the cracked software, the user winds up unknowingly installing the Botnet trojan as well, and placing the contents of their hard drive at risk, not to mention their sensitive information, such as passwords and even online banking login information.

So how can Mac users avoid contracting a software virus or trojan? While there are never any guarantees online, web security experts say that avoiding pirated or cracked software is the easiest way to minimize your chances of inadvertently installing malicious software on your Mac.

According to another online security company, Intego, as of January 2009, over 20,000 Mac users were known to have their computers infected with the Botnet trojan or other viruses. This, of course, is just a fraction of the number of PCs infected with malware; but it represents a sharp rise in the number of Macs affected over the past two years.

So the good news is, yes, Macs are still “safer” on average than PCs. The bad news? Malicious software for Macs is growing in number every year, and once infected with a virus or trojan, removing the malware from a Mac can be considerably more difficult than with a PC. And, unfortunately, as Apple continues to gain market share on Windows, it stands to reason that more and more hackers will begin targeting Mac computers.