Microsoft's offer of free Windows 10 upgrades for software pirates may have some strings attached after all.

Shortly after Microsoft revealed that it will allow upgrades for “non-genuine” copies of Windows, the company clarified to Ars Technica that these copies will remain illegitimate.

“With Windows 10, although non-Genuine PCs may be able to upgrade to Windows 10, the upgrade will not change the genuine state of the license,” Microsoft said. “If a device was considered non-genuine or mislicensed prior to the upgrade, that device will continue to be considered non-genuine or mislicensed after the upgrade.”

Terry Myerson, the head of Microsoft's operating systems unit, first announced the upgrade offer at a conference in China, where Windows piracy is widespread. Microsoft then confirmed that the upgrade would be available worldwide. The hope is that illegitimate users will “realize the value of properly licensing Windows and we will make it easy for them to move to legitimate copies,” the company said.

Microsoft is staying tight-lipped on the details, such as the cost to go legit, the drawbacks of a non-genuine copy, and whether pirated users can still get patches and security updates. The company simply gave a “no comment” when pressed for more details by Ars.

Why this matters: Microsoft is trying to have it both ways here. Windows 10 needs a healthy installed base to build up an ecosystem of modern apps and services, which is exactly why Microsoft is also giving away consumer upgrades to legit Windows 7 and Windows 8 users. Still, the company probably doesn't want to look like it's condoning piracy by letting illegitimate users off the hook. This is a difficult line to walk, as pirates could eye Microsoft's upgrade offer with suspicion, and may prefer to stay off the grid.