Apple has released Security Update 2010-007 and Mac OS X 10.6.5, each of which fixes a large number of critical vulnerabilities in Mac OS X and Mac OS X Server, some of which may lead to unexpected application termination or arbitrary code execution. For more information, see
Mac OS X 10.6.5 update is available for Mac OS X 10.6.x and Mac OS X Server 10.6.x. Security Update 2010-007 is available for Mac OS X 10.5.8 and Mac OS X Server 10.5.8.
Software Update will install either Security Update 2010-007 or Mac OS X 10.6.5, whichever is appropriate for your system.