[liberationtech] NSA Xkeyscore VPN reference question

[h0ost]

The pdf Xkeyscore document listed on the Guardian website (
http://www.theguardian.com/world/2013/jul/31/nsa-top-secret-program-online-data
) makes a reference on how the NSA can potentially decrypt VPN traffic
and user data.

Is there a sense on what this could mean?  Are they talking about
PPTP-based VPNs, OpenVPN, or any VPN protocols in use today?