For previous versions of Microsoft Windows, users can download updates from the Windows Update website, using Internet Explorer.
While details have changed from version to version, it has always scanned the computer to find what operating system components and software are installed, and compared the versions of those components with the latest available versions.
The Critical Update Notification Tool then compared this list with the list of installed updates on the user's machine, and displayed a message to the user informing them of new critical updates if they were available. Moore in early 1999 was critical of this approach, describing it as "horribly inefficient" and susceptible to attacks.
Once the check executed, any custom schedule defined by the user was reverted to the default; Microsoft stated that this was by design in order to ensure that users received notification of critical updates in a timely manner. In a posting to Bug Traq, he explained that, "every single Windows 98 computer that wishes to get an update has to rely on a single host for the security.
The Active X component then executes the downloaded installation files in their silent/unattended mode to install or update those components, and to report the success or failure of those installations back to Microsoft's servers.
The first version of the Windows Update web site (usually referred to as "v3") did not require any personally-identifiable information to be sent to Microsoft.