It's taken a while and a serious scare but it would appear that Apple has finally accepted that its aura of viral immunity is not impregnable. The arrival and rapid spread of the Flashback trojan has convinced Apple to be a little more forthright about security.
Many small businesses that we've spoken to prefer to run Macs for lots of reasons. Inevitably, one of the reasons we hear is that they are "more secure" than computers running Windows. The reality is that the Mac platform hasn't been a significant target until recently.
The folks that write and distribute malware these days have only one thing on their minds - profit. Put simply, when Apple's marketshare was smaller, there was little reward to be gained by duping a few people to part with their money. However, as Apple's market share has grown, so has the opportunity to profit by infecting Macs and either using them in botnets or stealing data from them.
In response to the changing threats, Apple has made some changes to its Mac publicity materials. Previously, Apple's messaging said things like "Safeguard your data. By doing nothing". That's been replaced with "Safety. Built Right in".
If you're using a Mac in your business, we'd argue that the time has come to find and install security software.