Microsoft has already declared that Windows 10 will be a free upgrade on its July 29 release date. And the offer is valid for the lifetime of a machine.

Users need to have Windows 7, 8 or 8.1 to be eligible. But what if these users want a clean install, to start over and wipe out everything to get rid of nagging PC issues? Will the software continue to be free?

Microsoft software engineer Gabe Aul appears to have the answer, according to a report by SuperSite for Windows. Aul took to Twitter this week to clarify that, even after a clean install, Windows 10 will remain free for qualified machines.

“Once you upgrade Windows 10 with the free upgrade offer, you will be able to clean reinstall Windows 10 on the same device at any time,” Aul said on a Twitter post Tuesday. The same report also indicated that the clarification applies to Windows 7 and later versions.

The Microsoft engineer added that starting over with Windows 10 can be done two ways -- by opting for the built-in Reset function of the OS or by using an ISO disk image of the software. In both ways, Aul told PC World that upgraders need not reenter the product key of the old Windows build they were running.

“Their devices will reactivate themselves after being upgraded to Windows 10,” the report said.

Aul did not touch on one likely complication. If a machine has upgraded components before July 29, will the offer stand? And what if hardware needs to be replaced in the months after the launch? Will Microsoft still honor the deal?

On this subject, the safest course is for users to implement hardware modifications before the scheduled Windows 10 rollout next month, PC World said. At any rate, Microsoft might be more accommodating in allowing upgrades, if only to realize its goal of putting Windows 10 on 1 billion devices by 2018, the report added.