Introducing the Innovator's Patent Agreement
Note: Emphasis is mine.
"We will implement the IPA later this year, and it will apply to all patents issued to our engineers, both past and present." [1]
"The Innovators Patent Agreement (IPA) is a new way to do patent assignment that keeps control in the hands of engineers and designers. It is a commitment from a company to its employees that patents can only be used for defensive purposes. The company will not use the patents in offensive litigation without the permission of the inventors. This control flows with the patents, so if the company sells the patents to others, the assignee can only use the patents as the inventor intended." [2]
[1] http://engineering.twitter.com/2012/04/introducing-innovator...