Another article, with more details:

Quote:
How Microsoft handed the NSA access to encrypted messages

• Secret files show scale of Silicon Valley co-operation on Prism
• Outlook.com encryption unlocked even before official launch
• Skype worked to enable Prism collection of video calls
• Company says it is legally compelled to comply


http://www.guardian.co.uk/world/2013/jul/11/microsoft-nsa-collaboration-user-data