Seemingly they are, sort of, in one of those round about "I'm going to see what I can grab" kind of ways.
Preliminary reports from /. suggest that Micro$haft are going after the patent to XML.
If anyone can make head nor tails of the actual article that is linked from here, please comment and clear this up. It's safe to say, whatever is going on, it's very strange, and odder still it's taken 3 years to come out that they did it.