Skype joined PRISM in 2011
Lets recap, lest we get a history re-write:
"Microsoft – which is currently running an advertising campaign with the slogan "Your privacy is our priority" – was the first, with collection beginning in December 2007....It was followed by ...Skype and AOL in 2011"
The PRISM document is recent (post Skype purchase by Microsoft):
"The document is recent, dating to April 2013."
On this slide it shows PRISM obtains data from Skype:
On the right the data that can be obtained from PRISM. Voip, chat etc.
Chess was the next revelation:
"Skype, the Internet-based calling service, began its own secret program, Project Chess, to explore the legal and technical issues in making Skype calls readily available to intelligence agencies and law enforcement officials, according to people briefed on the program..."
It's difficult to get a truthful answer out of people. For example, we know BULLRUN has a database of private keys available for attacks. We know that a judge authorized the FBI to grab Lavabits SSL keys. It seems likely those SSL keys go into BULLRUN database since NSA handles these intercepts. But the Judge only authorized a limited grab-and-filter on the promise that the rest would be thrown away. So any other use under Bullrun would violate his order. Yet as long as they keep it secret, how would the judge know? How would Lavabit know?
How many of those Bullrun keys were obtained in the same way, and violate other secret court orders?
(Bullrun, page 6 also mentions Skype.)