Windows Update is software designed to help keep your computer current and more secure by automatically downloading and installing the latest security and feature updates from Microsoft.
Windows Update determines which updates are applicable to your computer and can download and install them automatically to keep your computer up to date and more secure.
If you want to Turn on/off automatic updating in Vista follow this procedure
Click on Start>All Programs>Windows Update.
In the left pane, click Change settings.
Choose the option that you want and Under Recommended updates, select the Include recommended updates when downloading, installing, or notifying me about updates check box, and then click OK.
If you are prompted for an administrator password or confirmation, type the password or provide confirmation.