They laptop came originally with MS Vista Business. The seller, I believe, upgraded it to Windows 7 Ultimate. It is activated and it is legit according to Microsoft yesterday. It also has MS Office 2010.
Microsoft’s licensing is done by a randomly-generated algorithm based on hardware installed on the system. Make any major changes to your system, and you need to re-authenticate your OS license.
As long as the Microsoft software licensing sticker is somewhere on the laptop and the license number on the sticker is the same as the one used to authenticate the OS with MS, you’re fine from a Microsoft licensing perspective.
That doesn’t authenticate the legitimacy of the actual computer. You could go out tomorrow, steal your neighbor’s HP or Dell laptop, buy a $100 copy of Win7, wipe the hard drive, install the new OS, et voila, you’ve got a working computer. It’s still stolen, though.