The UK Government's Government Communications Headquarters (GCHQ) operated a top secret surveillance programme known as "Optic Nerve", which captured images from millions of Yahoo! webcam chats, and even spied on people while nude.
The vast majority of webcam feeds captured were from people who were not suspected of committing any crime.
The documents, leaked to the press as part of the vast treasure trove released in June last year by Edward Snowden, should put to rest any speculation that the worst of the spying allegations have already been leaked.
They reveal that Yahoo! was chosen by GCHQ because it was known to be used by "GCHQ targets", or potential terrorists.
The American National Security Agency (NSA) was also involved, providing software to identify Yahoo! video traffic online and make it searchable once it had been intercepted.
The images were collected and apparently used to conduct experiments in facial recognition technology, and also to detect criminals or terror suspects who were using multiple accounts to hold webcam chats.
One leaked document says: "Face detection has the potential to aid selection of useful images for 'mugshots' or even for face recognition by assessing the angle of the face. The best images are ones where the person is facing the camera with their face upright."
The documents were taken from GCHQ's internal wiki, and indicate that while the project was closed at the time of the documents' leaking, it was "shortly to return!"
Users will perhaps be most dismayed by the fact that GCHQ specifically remarks on the fact that it caught sight of some unwary users while they were in the nude, or sharing intimate moments over webcam.
"Unfortunately," the documents state, "it would appear that a surprising number of people use webcam conversations to show intimate parts of their body to the other person."
That's not all, though:
"Also, the fact that the Yahoo software allows more than one person to view a webcam stream without necessarily sending a reciprocal stream means that it appears sometimes to be used for broadcasting pornography."
The UK Government has yet to comment on the leaks, although ITProPortal has tweeted the Prime Minister directly for comment.