RedHat and Mandrake seem to be popular on campus. The aforementioned sites include updates for the respective vendors' operating systems and software applications. If you're running software not written or distributed by those vendors, you'll need to visit the applicable software vendors' sites for the packages you're running. You'll need to do this on a regular basis. For example, a bug allowing the possible compromise of a computer through the popular Adobe Acrobat reader was posted that wouldn't be found on the Microsoft or Linux web sites.
Some vendors offer automated email notifications of new security issues.
Individual software packages may also need regular updates. For example, Antivirus tools are designed to detect code patterns or behavior known to be associated with hostile code. People seem to constantly create new hostile code so, like a flu vaccine, antiviral tools must be updated in order to recognize the new code. If you login to a campus Novell Netware server, both your Norton and BOClean protective software will automatically update once they are installed. Otherwise, you will need to update the software yourself.