This is an interesting addition to the new OS X release.  Although no one really knows what it does exactly, it does add an interesting glimpse on how things are changing for Apple.  Here is a short write up i found:

We’ve gotten reports about an interesting feature in Snow Leopard, the new version of Mac OS X due for release this Friday. According to reports we’ve seen – and the screen shot below – Snow Leopard contains an antimalware feature.

We’re not sure yet exactly how this works, but the above screen shot shows this feature working with a download made via Safari, detecting a version of the RSPlug Trojan horse in a downloaded disk image.

We’re naturally curious about this feature, and about how thorough it is. As soon as we can find out more, we’ll post an article here. We wonder just how serious Apple thinks the malware threat is, especially since their latest Get a Mac ads highlight the fact that PCs running Windows suffer from viruses…

There are several things that I can see this stemming from. Probably the most notorious was the iWork 09, that came with a nice trojan. While it is a horrible reality that companies are having to take extra steps to protect their product form illegally downloaded torrents, I applaud them for taking the first step at least.

(Via Mac Security Blog)