The free Windows
Defender anti-spyware program (not for Windows 98 or ME) is worth
downloading if you have
already successfuly run the Microsoft ownership verification program.
If you have made any extensive changes to the hardware on your system,
such as installing a new motherboard, I do not recommend taking the
risk of letting the verification program mistake your legitimate copy
of Windows as being a pirated one. I would instead suggest you rely
only on the several other very good anti-malware scanning programs
listed on thse web pages.
Windows Defender can be downloaded (after the ownership check) from