Two updates have been released by Apple in the past week. One for QuickTime, which applies to both Mac and Windows PCs, and one for wireless networking in Mac OS 10.4.8. See Security Update 2007-001 and AirPort Extreme Update 2007-001 for more information about the patches.
To make sure your computer is up-to-date, you can run Software Update to check at any time. For instructions on how to run Software Update, please see Mac Maintenance on the Help Desk web site.
For those of you who read the Month of _____ Bugs entry, the QuickTime vulnerability was reported on the Month of Apple Bugs blog, and the AirPort vulnerability was reported on the Month of Kernel Bugs site.