One of the big plus points about owning a Mac is that feeling that you’re free from the continual virus threats that the majority of PC owners have to deal with. Not so anymore, according to security experts Sophos, who believe they have discovered the first virus for the Apple Mac OS X operating system.
The virus, known as OSX/Leap-A and claiming to feature screenshots of a new Mac operating platform, spreads via the iChat instant messaging system, forwarding itself as a file called latestpics.tgz to contacts on an infected users’ buddy list.
The impact of a Mac virus in existence is far bigger than the actual threat, which is rated as "low" by security firm Symantec. They suggest a number of basic security "best practices" for Mac users to follow on their website including turning off and remove unneeded services among other suggestions. I’d add to that common sense when dealing with unsolicited files or emails.
More information from Symantec