It seems that Snow Leopard contains some sort of anti-malware system. But what does it really protect you from? Not much.
It seems to scan for only OSX.RSPlug and OSX.Iservice and then only scans files from Safari, Mail, and a few web browsers. Usenet and Bittorrent clients are unaffected. It doesn’t even actively scan the Downloads folder.
So it’s basically like someone at Apple wrote an anti-virus program and just snuck it into Snow Leopard. You can just imagine some grizzled old programmer who has been working on this since 1994 finally getting his chance to shine.
Apple stuck the anti-malware software into Snow Leopard without actually announcing it. The software is invisible – it just kind of hangs out – and the only thing I see this doing is encouraging anti-virus software vendors to try to upsell their paltry OS X offerings. While Macs aren’t totally impervious to virii and trojanii, there is always the off chance that a piece of rogue software could fall into the mix. This could be a simple solution to preventing Snow Leopard Macs from falling into a botnet.