Windows Update clients normally download updates over an Internet connection, although Microsoft makes provision for installing updates on computers without an Internet connection and a range of alternative methods and programs also exist to install updates. Security updates or critical updates protect against vulnerabilities to malware and security exploits.
Other updates correct errors unrelated to security, or enhance functionality.
Windows Vista and later provide a Control Panel to configure update settings and check for updates.
The Windows Update Control Panel also has the function of downloading Windows Ultimate Extras, optional software for Windows Vista Ultimate Edition.
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 for those operating systems.
The initial focus of Windows Update was on free add-ons and new technologies for Windows; security fixes for Outlook Express, Internet Explorer and other applications appeared later, as did access to beta versions of upcoming Microsoft software, most notably Internet Explorer 5.
Initial releases of Windows 2000 shipped with the tool, but Windows 95 and Windows NT 4.0 were not supported.
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.Windows Update requires Internet Explorer or a third-party web browser that uses Microsoft's MSHTML layout engine, as it must support the use of an Active X control to house the software that is executed on the user's computer.