From Jonsdocswiki

WSUS is Microsoft's Windows Server Update Service and can be installed on Windows Server 2003 upwards to allow system administrators to download a Microsoft Update once (to the WSUS server) and then the update will be passed out to computers requiring it over the LAN. Implementing WSUS will save Internet Bandwidth (updates are only downloaded once).

Troubleshooting

Computers don't show in the WSUS console

• Firstly, check some computers have been powered on since WSUS was installed.
• If you have configured WSUS to assign computers to groups using client side targeting, check your Group Policy settings actually specify a group for the computers to be placed in.
  • You need to manually create the groups on the WSUS server first.
  • Names specified in client side targeting are case sensitive.
• Check only one group policy with the setting is being applied to the computer in question. More accurately, ensure only one group policy with this setting is at the applicable level.