Responsible for updating

Critical Update Notification Utility (initially Critical Update Notification Tool) is a background process that checks the Windows Update web site on a regular schedule for new updates that have been marked as "Critical". By default, this check occurs every five minutes, plus when Internet Explorer starts; however, the user could configure the next check to occur only at certain times of the day or on certain days of the week.

The tool queries the Microsoft server for a file called "", which contained a list of all the critical updates released for the operating system.

Fixes to Windows 98 to resolve the Year 2000 problem were distributed using Windows Update in December 1998.

Microsoft attributed the sales success of Windows 98 in part to Windows Update.

Instead, the app downloads a full list of every available update and chooses which one to download and install.

But the list grew so large that the performance impact of processing became a concern.

System administrators can configure Windows Update to install critical updates automatically, so long as the computer has an Internet connection.

Windows 95 and Windows NT 4 were retroactively given the ability to access the Windows Update website, and download updates designed for those operating systems, starting with the release of versions of Internet Explorer 4.The tool then compares this list with the list of installed updates on its machine and displays an update availability notification.Once the check is executed, any custom schedule defined by the user is reverted to the default. Moore in early 1999 was critical of this approach, describing it as "horribly inefficient" and susceptible to attacks.Arie Slob, writing for the newsletter in March 2003, noted that the size of the update list had exceeded Windows Update v4, released in 2001 in conjunction with Windows XP, changed this.This version of the app makes an inventory of the system's hardware and Microsoft software and sends them to the service, thus offloading the processing burden to Microsoft servers.Microsoft stated that this ensures 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.

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