Linus Torvalds, the man behind the infamous Linux kernel, has come out to retort at Microsoft's claims recently. Microsoft has been claiming that the Linux kernel, among many other pieces of software, violate their patents. Dozens of patents, in fact. Obviously, Linus was none to pleased to hear this. He isn't even going so far as to say he accepts any of it, calling the entire thing FUD. His comments make it pretty clear that Microsoft has made no moves:

Can you get a list of which ones? Before that, it's just FUD, and there's not a whole lot I can say or do. Is there prior art? Are they trivial and obvious to one skilled in the art? Would we need to work around them? We don't know, because all I've heard so far is just FUD.
If MS actually _wanted_ us to not infringe their patents, they'd tell us. Since they don't, that must mean that they actually prefer the FUD.

Will Microsoft push this further? It's certainly not the first time they have made these claims, nor will it be the last. It is truth, though, that they have never compiled a list of supposedly violated patents with which they intend to sue over.