B&N's Nook used Android. MS claims to have patents that cover Android stuff. MS wanted B&N to pay licence fees for that patented technology. B&N wanted to find out what exactly was covered. MS claimed that to disclose that information (which is in a public patent) they'd have to get B&N to NDA. Eventually, a list of patents arrive, and they're all for tiny stupid trivial stuff or for really old stuff; yet MS was trying to charge for them as if they were worth a full OS.
See this PDF for a list of the trivial patents:
(http://www.groklaw.net/pdf3/675085-463533.pdf)