Naked Security warns that users of Mac should be concerned about what might be hiding on their hard drive. "Sophos Anti-Virus for Mac Home Edition launched on Nov'2nd, proved instantly popular, and also made the list of top products downloaded on Apple site, and is listed as the most popular download in their Networking & Security section."
Sophos says they've 150K Mac users and of those nearly 50,000 have already reported finding malware on the computer -- "Mal/ASFDldr-A," that takes advantage of a flaw in Windows Media Player which allows the infected media file to open a malicious web page rather than display the desired content.
They found though that the majority of attacks detected were Java exploits which're cross platform and were typically found in the internet cache on users computers. But lower on the list they did find some OS X specific pieces of malware OSX/Jahlav-C and OSX/DNSCha-E. OSX/Jahlav-C is a variant of OSX/DNSCha-E which happens to be a piece of malware that known as a DNS changer. When a DNS changer hijacks your computers DNS settings your web surfing can be almost completely compromised. Even if it looks like you're at Google.com and the page looks like Google's home page your DNS settings may have sent you to a server in China where malicious code is being executed in your browser.
Here's a list of the most commonly encountered malware that these Mac users are seeing: