About Mac OS X 10.6.8 Update

The 10.6.8 update is recommended for all users running Mac OS X Snow Leopard and includes general operating system fixes that enhance the stability, compatibility, and security of your Mac, including fixes that:

Enhance the Mac App Store to get your Mac ready to upgrade to Mac OS X Lion

Resolve an issue that may cause Preview to unexpectedly quit

Improve support for IPv6

Improve VPN reliability

Identify and remove known variants of Mac Defender

See this article on how to verify the authenticity of this update.