Windows Update, a service offered by Microsoft, provides updates for Windows components. It can be replaced with Microsoft Update, an expanded version of the service which provides for other Microsoft software as well, such as Microsoft Office, Windows Live Essentials and Microsoft Expression Studio. 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.
The service provides different kinds of updates. Security updates or critical updates protect against vulnerabilities to malware and security exploits. Other updates correct errors unrelated to security, or enhance functionality.
Microsoft routinely releases security updates on the second Tuesday of each month (Patch Tuesday), but can provide them whenever a new update is urgently required to prevent a newly discovered or prevalent exploit targeting Windows users. System administrators can configure Windows Update to install critical updates automatically so long as the computer has an Internet mobile connection, without the user needing to install them manually, or even be aware that an update is required.
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. For previous versions of Microsoft Windows, users can download updates from the Windows Update website, using Internet Explorer.