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.
The initial focus of Windows Update was free add-ons and new technologies for Windows.
Security fixes for Outlook Express, Internet Explorer and other programs appeared later, as did access to beta versions of upcoming Microsoft software, e.g., Internet Explorer 5.
If that one server got compromised one day, or an attacker cracks the [Microsoft] DNS server again, there could be millions of users installing trojans every hour. Unlike its predecessor, Automatic Updates can download and install updates.
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.
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.
Enables the detection, download, and installation of updates for Windows and other programs.