Microsoft (NASDAQ:MSFT) wants to have its new Windows 10 operating system running on one billion devices within two to three years. One way it will accomplish that is making it easy and free for many (but not all) of its existing customers to upgrade.

In addition to clearing a path for current Windows 7 and 8 users to get the news OS, the company has also opened the door to allow people with pirated versions of operating system to get Windows 10. It's not quite free Windows for everyone, but it's a plausible way to bring people using an illicit version of the OS into the fold.

Windows 10 will be released on July 29. Source: Microsoft

How do you get Windows 10?
There are a number of paths for computer and tablet owners to make the upgrade to Windows 10. The easiest one is offered to people running legal copies of Windows 7 or 8. For those users upgrading is free and in many cases an icon is already appearing on your screen allowing you to register ahead of the July 29 launch. Signing up in advance allows some files to download before the release date which should make the process go faster at launch. Legal Win 7 and 8 users can also decline the opportunity to preregister and upgrade for free after or on July 29.

Legal users of older Microsoft operating systems including Vista and XP do not qualify for the free upgrade. If they want Windows 10 for free, they will have to follow the same path as people running illegal or unlicensed versions of the OS.

How to make pirated Windows legal
At one point Microsoft announced that people running pirated versions of Windows 7 or 8 would qualify for the free upgrade, which would then become a legal copy. The company later clarified those comments and explained that people running pirated or older versions of Windows could not get the free, full-legal edition.

But in closing a door the company opened a window as it is allowing people who don't qualify for the free upgrade to remain in the Windows Insider program. Those users won't get the stable, finished version of Windows 10; instead, they will continue to get new builds of the OS a little bit ahead of their release to to the public at large.

The company explained its offer in a blog post:

If you want to continue as a Windows Insider past 7/29 there is nothing you need to do. You're already opted in and receiving builds in the Fast or Slow ring depending upon your selection. This is prerelease software and is activated with a prerelease key. Each individual build will expire after a time, but you'll continue to receive new builds so by the time an older prerelease build expires you'll have received a new one. Since we're continuing the Windows Insider Program you'll be able to continue receiving builds and those builds will continue to be activated under the terms of the Windows Insider Program.

With past releases of Windows Microsoft discontinued the preview program with the launch of the new OS. In the case of Windows 8, which I had installed on a machine, which was originally running XP, I was sent a notice as to when my Win8 build would no longer work and an offer to upgrade.

In the case of Windows 10, Microsoft appears to be keeping the testing program open for the long term, though it does not promise to do so forever. 

What exactly are you getting?
People who choose to remain in then won't have a very different experience when the OS formally gets introduced on July 29.

As part of the program we'll upgrade Insiders to what is for all intents and purposes the same build as what other customers will get on 7/29, but that will be just another build for Insiders, and those who stay in the program will simply get the next build after as well.

People who remain in the Insiders program have to agree to keep installing new versions as they are released. This can be a bit of a double-edged sword where members get to see new features first, but those features may be glitchy or cause system crashes.

In general, though, as someone who has been a member for Windows 8 and 10, the Insiders program gives you a workable OS that grows more stable as the actual release date approaches. It's likely that any postrelease updates won't greatly impact that stability.

Is this a good deal?
It's an excellent offer especially because many people running nonlicensed or pirated copies of Windows likely do not know they are doing so. For example, I had a Dell laptop that I purchased on eBay. The machine worked fine until it didn't and it would only give me the blue screen of death. A phone call to Dell to get recovery discs led to me learning that the previous owner had purchased the laptop with Linux installed.

Though it had Windows stickers and looked legitimate, my OS had been pirated. That meant I was not entitled to recovery discs, which left me no (legal) way to reinstall Windows. That forced me to purchase a copy of Windows 8 to bring the machine back to life. Had the Insider Preview been offered, I gladly would have accepted being a bit of a guinea pig in exchange for the free OS (especially because I now have that computer running the preview of Win 10 anyway).

While running a preview version of the OS is not quite as good as getting a free, fully stable copy, it's still a good deal for people who do not qualify for the upgrade.

Daniel Kline owns shares of Apple and Microsoft. He does not look good in an eye patch. The Motley Fool recommends Apple and eBay. The Motley Fool owns shares of Apple and eBay. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.