Microsoft has been using a deceptive tactic to dupe Windows 7 and Windows 8.1 users into upgrading to Windows 10 for at least the last two months, according to the company's website.

An oft-revised support document that Computerworld cited in a May 16 story about Microsoft's aggressive upgrade practices spelled out the workings of a pop-up notification that Windows 7 and 8.1 users had been seeing. The notification told those customers -- primarily consumers, but also many small-to-mid-sized businesses -- that the free Windows 10 upgrade had been pre-scheduled by Microsoft.

The same document also acknowledged that those who clicked the red "X" in the upper-right corner of the pop-up were approving the scheduled upgrade.

"If you click on OK or on the red 'X', you're all set for the upgrade and there is nothing further to do," the document stated.

The problem was that that operation -- clicking the X -- has been a decades-old convention in graphical user interfaces (GUIs) for simply closing a window. To users, shutting a window by clicking the X tells the operating system or application to remove the notification or close the window frame without expressing an opinion, without selecting an option or without calling for an action.

In an application like Microsoft Word, for example, clicking the X closes the window: If Word did not remind the user to save his or her work, all content would be lost.

Plainly put, users have been "trained" by operating systems, including Windows, to click the "close" button to do just that, and nothing more. (In OS X, the action is conducted a bit differently -- one clicks on the red, left-most button at the top of a window -- but the behavior is identical.)

Yet Microsoft bucked convention by instead equating closing the window with approving the scheduled upgrade. Because there are no explanations to that effect in the pop-up -- only in the support document -- it's highly likely that the vast majority of users who clicked on the X to make the notification disappear had no idea that they were, in fact, authorizing an upgrade to Windows 10.

But while Computerworld first mentioned the practice on May 16, Microsoft has been counter-intuitively interpreting the action for months.

A version of the same support document found in a search engine cache last week revealed that Microsoft has been using the tactic since at least late March: The cached document carried a "Last Review" date stamp of March 23.

That document also noted the Bizarro World way of construing a click-on-X.

"Your Windows 10 upgrade will occur at the scheduled time if you close this window without either selecting Upgrade now or by using the link to change the upgrade schedule or cancel the scheduled upgrade," the document read [emphasis added].

It's unclear how long before March 23 Microsoft was defining an X-click as approving the pre-scheduled Windows 10 upgrade.

Not surprisingly, the reaction from users has been brutal.

Long-time Microsoft watcher and blogger Paul Thurrott today called the practice "indefensible" and said "I've had it." Brad Chacos, a senior editor at PCworld -- like Computerworld, a publication owned by IDG -- dubbed it a "dirty trick" and related how his wife, a dedicated Windows user, was so angry at the scheme that she had started shopping for a Mac Mini from Apple.

Even self-professed fans of Windows thought Microsoft had gone too far in pressing people to upgrade.

"Windows 10 is, in my opinion, a great OS, and the fact that it's free to upgrade from 7 and 8 is just awesome," said someone identified as zeynl on Sunday in a long Reddit thread on the X-clicking practice. "But the fact that Microsoft will go this far to get it onto peoples' systems is disgusting."

"I like Windows 10, but this...is just wrong," added TheJewelOfJool last week, also on Reddit.

"Wow. Even for Microsoft, that's a new low," said AI221 on Reddit today.

Some, though, essentially told everyone to suck it up and take the upgrade. "I find it amusing that people are fighting this so hard for nothing," countered XxSliphxX yesterday. "[Windows] 10 is pretty awesome just f****** update and stop being massive hipsters about it."

Within the pop-up, the only way to avoid the upgrade, according to Microsoft, is to click the one-word link highlighting "here" in the line, "Click here to change upgrade schedule or cancel scheduled upgrade."