Apple traditionally has not been a target of hackers, yet that may be changing. Two articles this week note that increased popularity and some specific security holes in programs pose potential weaknesses.
Jeremy Kirk, at PC World, "explains":http://www.pcworld.idg.com.au/index.php/id;1308570884 that increased popularity of the operating system correlates to increase likelihood for attacks. Apple has been actively releasing security updates and several companies have developed products for OS X security.
PayPal has "recently requested":http://arstechnica.com/journals/apple.ars/2008/02/29/paypal-to-safari-us... that users transition away from Safari. The program does not provide adequate phishing protection. "Michael Barrett":http://www.pcdoctor-guide.com/wordpress/?p=4678 a Senior Researcher at Paypal, and a StopBadware board member, had this to say: "Our recommendation at this point, to our customers, is use Internet Explorer 7 or 8 when it comes out, or Firefox 2 or Firefox 3, or indeed Opera."
Just goes to show that vigilance (and downloading security updates) is important for all operating systems available.