We intend to collect information on patching and keeping up-to-date all sorts of operating systems here.
Ideally, the OS's used by all of our end users will be covered.
Mac OS 9

Mac OS 9 contains its own mechanism that keeps itself up to date.
Locate your system's
Control Panels; usually, this is under the "Apple Menu"
in the upper left corner of your screen.
Among them, you should find a panel called
Software Update
(its icon is shown here).
Open that panel, and
from there you can check your system, schedule automatic updates, and so on.
Mac OS X

Mac OS X contains its own mechanism to keep itself up to date;
this applies to version 10.1 and all subsequent versions.
Open the
System Preferences
application (its icon is shown here), and in the row labeled
System,
look for
Software Update.
Click that pane, and
from there you can check your system, schedule automatic updates, and so on.
Solaris

Patch procedures applying to all recent (Solaris 2.6 through Solaris 9) are
covered in the
PatchingSolaris topic.
Note that most people with a Sun workstation on their desk in CIS
are not required to patch their machines; the CIS support staff takes care
of it remotely for you.
These instructions are really intended for self-maintainance or home users.
Windows

Patch procedures for Windows XP, Windows 2000, Windows NT, Windows Me, and Windows 98
will be found in the
PatchingWindows? topic.
Information regarding the recent Windows virii and worms (with exploits named
Blaster, Nachi, Stealther, and so on) is present in the
WindowsPatchProcedures topic.