How to detect if a Windows version is legal or not? [closed]

It's an interesting question but wrong attitude. It is not your business checking the affairs of the user.

Or you might as well:

• Require their tax declaration before selling your software to them

• A written proof from police they have no criminal record (or they may be inclined to break the law again and pirate your software)

• Check if they have any torrent software installed (of course it can be used legally but the very fact they have it implies they may misuse it)

• Check if they have antivirus software installed (to raise their social awareness and to help fight spam bot networks)

• A credit history report (to be sure they have promptly paid their bills and will also not forget to pay for your software)

• A proof from their family doctor they have no terminal disease (a person feeling condemned may break the law and pirate your software)

You see where it's going right?

One of the key rules for developing software - your software should be useful, make the users happy and build as few barriers as possible.

You can't possibly know and you shouldn't care.

The legal status of an install is entirely unrelated to anything on the disk. The same install can be unlicensed now and licensed the next minute without any changes to the machine.

That's something for Microsoft to worry about. Not you.