Traditionally, many users of Mac OS X have thought themselves at a much reduced risk of attracting malware due to it being less widely used than Windows. As Macs have gained popularity and Mac OS X's market share has increased, it has caught some unwanted attention from blackhat hackers. Most of the exploits thus far have been from what the security community likes to call "script kiddies". It would seem that now the attacks are now starting to become more sophisticated.
Security firm Sophos has highlighted the recent development of a trojan called OSX/MusMinim-A, which it believes is indicative of a growing trend of the underground hacking community taking note of Apple's growth and spreading their targeting accordingly. The trojan is a remote access exploit which fools a user into entering their administrator password allowing the hacker to gain control of the computer. The trojan is very basic at this stage but its development shows that the era of infallibility for Mac is coming to an end. Another widely seen example is the RSPlug.A trojan which has been in the wild for quite sometime, which purports to be a plugin required to view a video file but modifies the DNS settings, redirecting users to malicious websites.
Many would argue that with the advent of Snow Leopard in August 2009 that malware protection has been built in. However, in testing, Sophos demonstrated that the malware protection in Snow Leopard would only defend against threats via Safari. When the RSPlug.A malware was placed on a simple USB key, it was not blocked from running.
It is critical if you are not running anti-virus software on your Mac that you seriously consider doing so. As we move forward, if Apple continues to gain traction in the personal computer market, the situation with malware will reach a point where the volume seen reaches parity with Windows.