Microsoft withdrew downloads for its latest official edition of Windows 10, version 1511, after it meddled with people's privacy settings.

Earlier we reported how Redmond disappeared the update, which could be fetched via the official media creation tool (MCT). The download became available in mid-November after Microsoft announced it as a major upgrade for Windows 10.

MCT is aimed at IT professionals and enthusiasts juggling many PCs: rather than have each computer upgrade to the latest build of Windows 10 via gigabytes of Windows Update downloads, you can instead download and create a single .ISO image of the operating system via MCT, write the image to a DVD or USB stick, and install the software on as many machines as you're licensed to.

So if you wanted to bring a bunch of Windows 8 machines up to the latest Windows 10, you'd pop into each of them a DVD or USB stick built from the latest MCT download, and save yourself a lot of time and bandwidth.

So when the November MCT download vanished over the weekend, it was a pain in the ASCII for people – it forced folks to install the July launch edition and then apply loads of patches from Windows Update across the board. (If you've already got a single Windows 10 computer and are upgrading via Windows Update, none of this really affects you; you'll get version 1511 soon, if not already, automatically.)

Now Microsoft's finally come clean on why it yanked the self-contained download of Windows 10 version 1511.

According to Redmond on Tuesday, "when the November update was installed, a few settings preferences may have inadvertently not been retained for advertising ID, Background apps, SmartScreen Filter, and Sync with devices."

Fair play to Microsoft for shedding light on the blunder. Basically, its operating system allowed apps to access people's unique advertising ID numbers; the SmartScreen Filter that sends executables to Microsoft servers to analyze was enabled; software was allowed to run in the background; and settings and passwords would be backed up the cloud. If you previously disabled any of those, they would be reenabled by the MCT-derived upgrade over a previous Windows 10 install.

So in effect, installing version 1511 of Windows 10 via the MCT on Windows 10 machines overwrote the user's privacy settings.

"Recently we learned of an issue that could have impacted an extremely small number of people who had already installed Windows 10 and applied the November update," a spokesperson told The Register on Tuesday.

"Once these customers installed the November update, a few of their settings preferences may have inadvertently not been retained. For these customers, we will restore their settings over the coming days and we apologize for the inconvenience. We worked to resolve the issue as quickly as possible – it will not impact future installs of the November update, which is available today."

Indeed, this update is supposed to correct the overwritten settings. Microsoft has come under fire for its odd approach to privacy in Windows 10, but at least in this case it acted fast fixing the cockup.

The November update, version 1511 aka build 10586, is now available again via MCT for people with machines to manage. ®