Apple has reportedly been refusing to help hapless Mac users that inflicted this malware on themselves, by deliberately (being tricked into) installing this malware on their Macs.

Now it seems that they have had a change of heart, and are providing warnings about this malware, instructions for removing it, and will be issuing a tool to remove it automatically via Software Update in the near future.

They were slow on the uptake, but good for them for coming around!

How to avoid or remove Mac Defender malware - Apple.com

And yes, while this is not really a virus, because the user deliberately installs it, including giving their administrative username & password, that is not much solace to those that fall for it.

So, should Mac users start running anti-virus software? I don't see a need for it. Rather, they need to think about what they're doing.  For more information on some tips, see my previous article:

Mac OS X social engineering attack and general computer security guidelines