This [1] is one of my favorite leaks from Snowden revelations, and I regularly bring it up anytime people try to downplay what PRISM is. That's a user manual for NSA agents on how to spy on Skype users (including video and text) in real time. It's informative and also amusing at times. For instance in the FAQ one issue a confused spook might run into is why they're being spammed with the same messages repeatedly. It turns out that when a user logs on to a new device, the recent messages Microsoft sends to the user are also directly forwarded to the NSA, which can result (from their perspective) in messages being repeated.

[1] - https://www.aclu.org/sites/default/files/field_document/Guid...