Apple has released Mac OS X Snow Leopard 10.6.6 today, mainly for the Mac App Store integration, as well as one documented security fix.
Available for: Mac OS X v10.6 through v10.6.5, Mac OS X Server v10.6 through v10.6.5
Impact: A man-in-the-middle attacker may be able to cause an unexpected application termination or arbitrary code execution
Description: A format string issue exists in PackageKit’s handling of distribution scripts. A man-in-the-middle attacker may be able to cause an unexpected application termination or arbitrary code execution when Software Update checks for new updates. This issue is addressed through improved validation of distribution scripts. This issue does not affect systems prior to Mac OS X v10.6. Credit to Aaron Sigel of vtty.com for reporting this issue.
Mac OS X 10.6.6 is available on Apple's Software Update and also available as Combo download from Apple Support Download page.
Mac OS X v10.6.6 Update (143.59 MB)
Mac OS X v10.6.6 Update Combo (1.06 GB)
UserAgent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:18.104.22.168) Gecko/20101203 Firefox/3.6.13