From CIT Wiki
System and Network Security Guidelines
Unless you've received specific instructions from your application vendor to the contrary, we encourage you to make use of the automatic update features of Apple Macintosh and Microsoft Windows operating systems. As updates and security patches are made available from the developers, they can be automatically downloaded and applied to your system, including server operating systems. While many updates require rebooting the system to complete installation, you can continue to restart the computer on a schedule convenient to you and your department, but please be sure to finish the update installation as soon as is conveniently possible.
If you prefer to manage these updates manually, you can use online tools to scan your system, select the necessary updates, and apply them when it is best for you. We strongly encourage you to perform updates at least weekly. Even Apple has been providing critical system updates on a frequent basis recently. Here are the places you want to check: Microsoft Windows Update will require you to use Internet Explorer version 6 or better; an update to IE is provided on the page if you need it. Click here for instructions on using Windows Update. Note, this site as yet does not automatically apply updates to Microsoft Office or other Microsoft applications, nor does it update non-Microsoft applications at all; you'll have to check with the developer's site for those. The Microsoft Office updater can be found here, for now. Click on the button, "Click for Updates." Windows Update will also offer you the option of updating to "Microsoft Update" which included Office and other Microsoft applications in the update process.
Apple provides many troubleshooting tips, documents, and download links for specific models and applications all selectable from their main support page. Software updates in particular may be located on the download page, although this list contains downloads for many different versions and applications, sorted by date of release; not the most convenient organization. To check for updates to OS X, please follow these instructions. OS 9 users do similarly; open the Software Update control panel, click "Update now." You can have Software update check automatically. It will not check for updates to non-Apple software, you must do that on your own from the developer's site.
For now, we must presume that if you're using Linux, you know about obtaining and installing packaged software and updates. Check with your distribution and online resources for news and updates as they become available. Users of SuSE Linux, whether Professional or Enterprise Server editions, please note that support can be obtained from Novell's patch download site.
For more resources and links to govenmental, higher education, and other security sites, as well as the Common Criteria benchmarks and testing tools, please check the industrial tools page
