Unless you select the proper options, Windows XP's Automatic Updates service will download security updates and install them at a specified time, in the "background", without your involvement.

Within a few months of its May 2008 introduction, SP3 will be distributed via Automatic Updates; so make sure that its settings let you manage what is installed.

I just discovered a tool from Microsoft that prevents installation of service packs obtained with Windows Update.

The tool can delay the installation of Windows XP Service Pack 3 until May 2009. It can also be used with Vista SP1 and future service packs for Windows Server 2003. It only works with Windows Update and cannot stop the installation of service packs from CDs and DVDs.

The Windows Service Pack Blocker Tool Kit can be downloaded from Microsoft's website:

http://www.microsoft.com/downloads/

Just in case you are confused about Microsoft's terminology, here are some definitions:

Automatic Updates is an operating system service accessible from your computer's Control Panel. In its most automated mode, it does not require the use of a browser to download and install a Microsoft-recommended update.

Windows Update is an interactive program on Microsoft's website. Windows Update examines your computer and advises you of the updates available for your operating system. You must use Internet Explorer to access Windows Update.

Microsoft Update also requires Internet Explorer and is almost identical to Windows Update. Microsoft Update scans your computer and provides you with a list of updates for Microsoft applications such as MS Office.

Windows XP Service Pack 3 became available from Windows Update on May 6, 2008. On July 10, 2008, Microsoft started SP3's distribution via Automatic Updates.