Via email:

In order to provide customers with improvements in reliability, operation and service quality, Microsoft needs to occasionally update the infrastructure of the Windows Update client itself (this usually occurs about once a year). To help customers prepare, and ensure that they understand what’s happening, we have created several resources to provide information on the updates before they begin in late July.

This particular update will not make any changes to the way WU looks of feels, but will improve:

  • The length of time it takes Windows Update to scan for updates
  • The speed in which signature updates will be delivered

Windows Vista customers who select “never check for updates” (and Windows XP customers who select “turn off Automatic Update”) in their WU settings will not receive this WU infrastructure update unless they elect to install it manually by visiting Windows Update.

For more information about this particular infrastructure update, or for additional information on Windows Update, please visit:

Microsoft Update blog
Windows Update web pages
KB article