Apple Just released a new Security Update “Security Update 2008-07″ that can be downloaded from software update under the apple logo pull down menu from your mac : 

Security Update 2008-007 is recommended for all users and improves the security of Mac OS X. Previous security updates have been incorporated into this security update.

For information on the security content of this update, please visit this website:http://support.apple.com/kb/HT1222.

Source : Apple.com