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 here: