Microsoft will offer a free upgrade to Windows 10 to users running pirated copies of earlier editions.

The company also narrowed the launch date of the upgrade to "this summer," although it did not get more specific than that. Previously, the firm has said it would release Windows 10 this fall, which most experts interpreted as October because of past debut dates.

Reuters first reported on Microsoft's plan to offer Windows 10 free of charge to pirates.

The company is going to upgrade "all qualified PCs, genuine and non-genuine, to Windows 10," Microsoft confirmed today, reiterating what Terry Myerson, the chief of Microsoft's operating systems group, told Reuters. "Non-genuine" is Microsoft-speak for illegal copies.

The move would be unprecedented for Microsoft, which has spent years, devoted significant resources and developed numerous technologies to battle piracy, notably in the enormous Chinese market, where an estimated three-fourths of all installed software is pirated.

"They've done 'get legal' programs before, but those have always come with some kind of cost," said Michael Silver, an analyst with Gartner, referring to various initiatives, including one in 2007 aimed at prompting users to buy legitimate licenses.

Microsoft elaborated in a statement. "Anyone with a qualified device can upgrade to Window 10, including those with pirated copies of Windows," a company spokesperson said. "We believe customers over time will realize the value of properly licensing Windows and we will make it easy for them to move to legitimate copies."

It was unclear what limitations, if any, Microsoft meant with the "qualified device" comment.

The free Windows 10 upgrade will be offered to devices running Windows 7 or Windows 8.1, but not those running older editions, including the now-retired Windows XP or its flop of a follow-up, Windows Vista.