"Apple's recent introduction of the Mac mini, a $500 computer sold without a display, keyboard or mouse, could actually increase the likelihood of more malicious software computer code targeting the Mac platform, Symantec said. . . ."The market penetration of Macintosh platforms will be accelerated by the much lower priced Mac mini, which may be purchased by less security-savvy users," the report said. "As a result, the number of vulnerabilities can be expected to increase, as will malicious activity that targets them."
Symantec said that over the past year, it had documented 37 high-vulnerabilities -- weaknesses that leave the system open to malicious software attacks -- in Mac OS X. They "have been confirmed by the vendor, which, in the Apple case, almost always means that the company has released a patch."
This is a mere PREDICTION of future potential problems from a company that makes its money from FUD... and who wants to have Mac users buy its software. It says that 37 security issues have been found in OSX in the past year... all patched by Apple as soon as discovered. There is still not one example of a malicious exploit in the wild.
As with Wintel machines, quite a number of Mac virus attacks take place due to vulnerabilities in other software, such as the MS-Office suite of programs, or IE.
Personally, the only attacks on Mac OS-based computers that I've seen have been in threads like this. ;')