- Security/Critical Updates: These updates are important and should be applied as quickly as possible. The updates usually closes holes that could allow unauthorized people to get access to your computer.
- BugFix Updates: These updates are made for correcting some of the strange behavior Windows has. They are usually only released to the public through Service Packs.
- Recommended Updates: These updates usually add new features to the existing components or add completely new components. They are usually followed by some Security- and BugFix-Updates.
Microsoft Windows is a very complicated piece of software, and since the expense of finding all bugs before a release is quite high (and quite impossible), then Microsoft (and other software companies) releases their software when it is functional even though it has known bugs.
Related Windows 98 SE - Service Pack