This isn't the first time Microsoft has gone on the offensive against Android via the legal route.
Microsoft sued Motorola on October 1 over alleged infringement of Motorola’s Android smartphones on Microsoft’s patents. On November 9, Microsoft sued Motorola again over wireless and video coding patents that are used by the Xbox and smartphones. In the latter case, Microsoft claimed that Motorola is charging excessive royalties for its patents. Motorola has countersued Microsoft, for those keeping score at home.
HTC paid an undisclosed amount to Microsoft in 2010 to head off potential Android-based patent problems. HTC agreed to pay Microsoft an undisclosed sum to license Microsoft patented technology for use in phones running the Android operating system, Microsoft announced on April 27, 2010.