When Microsoft first deployed the update Feb. 8, it said the patch would be offered as an optional download. To retrieve it, users had to manually checkmark the "KB971029" update in the "Software, Optional" section of Windows Update in XP, or in Vista's Windows Update panel under "Important."

But last week Microsoft changed those rules and began feeding users the update through the Automatic Updates feature of Windows Update, which automatically downloads and installs hotfixes and other software upgrades. In Windows XP, for example, users now see the AutoRun fix under the "High-priority updates" label, and the patch is pre-checked so it downloads and installs without any user action.