Windows is installing "surprise updates" against the wishes of some users, who have expressly set up the operating system not to deploy patches without permission, researchers claim.
Numerous readers of the popular Windows Secrets newsletter have reported that they have watched their PCs install updates from the June 9 set of security patches as they've rebooted or when they've turned on their machines, said Brian Livingston, the newsletter's editorial director.
Those users have set options in Windows Update (WU), the operating system's default update service, to require their go-ahead before installing patches, or before downloading and installing updates.
"If you have an incomplete update download, Windows won't display the fact that you have updates," said Livingston, referring to the icon in the taskbar that should appear when updates are pending approval. "Then at shutdown or reboot, those updates start installing, even though the user has set Windows Update not to do so."
Only users who have set WU to the 'Automatic' setting should have patches downloaded and installed without any additional action on their part.
Windows Secrets staffers, including Livingston, have observed the surprise updates, although they have not been able to reproduce the bug, Livingston acknowledged. The bug affected users of both Windows XP and Vista.
Livingston speculated that the surprise installs were due to the record number of updates Microsoft issued on June 9. The collection of 10 security updates delivered a record 31 individual bug patches, the most in a single month since the company began regularly-scheduled updates in 2003.
The large number may have exceeded Microsoft's server capacity, which in turn may have resulted in some downloads failing before they were finished. "The 10 security bulletins may have created server overload that affected more people than usual," said Livingston.
Partial downloads are, in fact, a known issue with Windows Update. "Microsoft already has a Knowledge Base document that says if a download doesn't complete, then Automatic Updates terminates, and the remainder [of the update] is updated a few days later," Livingston said.
He pointed to a Microsoft support document that admits incomplete downloads can disable the usual display of the notification icon in the Windows system tray.
A Microsoft manager denied that the surprise-update issue was a bug, and said it was essentially business-as-usual. "The behaviour we expect to see is for users to be notified about updates that are available for them to install," Paul Pottorff, a senior product manager with the Windows Update team, said in an email sent to Computerworld US as well as Windows Secrets.
"[But] if there is only a throttled update, they shouldn't be notified. This behavior has been the same for a long time and hasn't even been touched for more than nine months."
This isn't the first time that Microsoft has been rebuked for installing updates without users' permission. In September 2007, Windows Secrets took the company to task for secretly updating files related to Windows Update itself; Microsoft said the concerns were unwarranted.
Later, Microsoft confirmed that the stealth WU update crippled some Windows XP machines.
Windows Secrets offers more details about the bug, as well as workarounds, on its website.