Leaked documents from the US National Security Agency (NSA), provided by Edward Snowden and published on Sunday by German newspaper Der Spiegel, show that the NSA has full access to traffic over Skype. That includes voice calls, video calls, instant messaging, and file sharing from specific persons of interest, and was granted by a Foreign Intelligence Surveillance Court warrant as part of the PRISM program.
A document from 2012, unambiguously titled “User’s Guide for PRISM Skype Collection”, details how to use the NSA’s NUCLEON system to task the capture of voice communications, and how PINWHALE is used to collect data from text chat and shared files.
Voice traffic capture began in February 2011 – the same year Microsoft bought Skype – for both “Skype in” and “Skype out” calls pertaining to specific users. In July of the same year the NSA gained access to peer-to-peer Skype communications, with Microsoft, under warrant, providing the keys it needed to decrypt the data.
Source: Ars Technica