Soon to arrive in Ballmer's inbox.
We notice that your Bing search engine is currently violating 235 of our patents. This could result in various legal headaches for not only you, but your customers and anybody that licenses any violating technology from you. We're not going to tell you which patents we have identified you as being in violation of, but rest assured that our legal team has assured us that we have a very solid case.
We are reasonably compassionate though. We suggest that you leave Android and its associated Linux kernel well alone, and pay us a yearly license fee of (insert seven figure sum here). In return, if we do decide to start suing anybody, we will look the other way as far as your products are concerned.
Yours very VERY cheerily