Which is what, exactly? Even Ballmer's pulling a McBride. You'd think he would've learned from SCO's mistakes.
Ask the senior counsel at the FSF, he enumerated 283 possible violations in the kernel alone. I read somewhere the Microsoft patents included in that were around 2 dozen.
To be fair, all 5,802 issued Microsoft patents are available to the public, as published by the USPTO. Comparing the code base to the issued MS patents would answer the question what, if any, patents are being infringed. But whose job is that?
On one hand, Microsoft could do the comparison. On the other hand, I would think it prudent for a company to conduct an IP landscape survey to understand liabilities (if any) in bringing a product to market.... but hey... that's just me.