Version 10.6.1 includes an update to Adobe Flash player. Hackers are increasingly targeting earlier versions of the software plug-in to exploit vulnerabilties fixed in later versions.
The first release of Snow Leopard would have overwritten Adobe Flash Player with a slightly older version that was more vulnerable to attack than the latest version from Adobe.
The Snow Leopard update also fixes a host of compatibility issues with Sierra wireless 3G modems, some printer drivers, keyboard shortcuts, mail servers and multimedia software.
Snow Leopard Server 10.6.1 includes all these fixes as well a fix for servers with multiple network interfaces reporting a duplicate serial number in use.
The update can be accessed using Software Update in Snow Leopard or from the Apple download site.