Microsoft's consumer security software changes the AU (Automatic Updates) settings in Windows XP and Vista without telling users or getting their approval, a researcher said Thursday -- behavior that may explain recent reports of patches being installed and systems rebooting without permission.

When Microsoft responded to new charges of silent changes last week, however, it denied that AU settings were ever altered without user approval, and it didn't mention OneCare as a possible culprit.

Scott Dunn, an editor at the "Windows Secrets" newsletter, reported Thursday morning that OneCare silently changes AU settings as it installs. No matter what AU setting the user selected previously, OneCare's installer quietly changes it to the fully automatic option.