Adware sample targets Mac OS X

Looks like I bought a Mac just in time. I never bought the “Apple Computers are immune to viruses, adware and other annoying Internet trickery”, because people are resourceful and will crack most any code. I always chalked it up to the fact that Apple has a 5% market share and it’s not worth anyones time to infect macs. Well, it seems the times may be changing, as CNET is reporting a sample Adware program is able to install itself on OS X machines without administrative rights. I have also recently read about proof of concept kernel and similar viruses for the Mac. Should I be thinking about buying anti-virus software for my new MacBook?