The Trojan construction kit for Mac OS X "is the first of its kind to hit the Mac OS platform," Peter Kruse, a partner and security specialist at the security firm CSIS, writes in his blog.
Why is the kit appearing now? Because Mac OS X is finally popular enough so that it's a tempting economic target. A paper back in 2008 estimated that Mac OS X would be targeted when it reached 16% market share --- which is what it now has in several countries, including the U.S.
Adam O'Donnell, chief architect of the cloud technology group at SourceFire, notes that "What is happening is that people are testing the waters. It just becomes economically viable to do it, so you start seeing these attacks becoming more common."
While Mac OS X may be becoming more vulnerable, Windows, at least according to Microsoft, is getting safer. The latest Security Intelligence Report from Microsoft claims that Windows 7 is far safer than previous versions of Windows. (Download the full report here.) The report found that Windows XP SP3 32-bit machines have an infection rate of 15.9 for every thousand systems, and Windows Vista SP2 32-bit PCs have a rate of 7.5 infections per thousand. Windows 7 32-bit computers have infection rates of 3.8 per thousand, and Windows 7 64-bit PCs have a rate of 2.5 per thousand.
That means a Windows 7 32-bit PC is more than four times more secure than an XP machine.
All this means that the days of Macs being far more secure than PCs may be coming to an end. Today a Mac is still safer than a Windows 7 computer. Whether Macs will be safer than PCs a few years from now isn't so clear, though.