A US court has ruled that Google must divulge the viewing habits of every user who has ever watched any video on YouTube. The decision comes as part of Google's legal battle with Viacom over allegations of copyright infringement.
YouTube is owned by search giant Google
What has the court ruled?
The US court has ordered Google to hand over the "logging database" which is updated each time a video is watched on YouTube.
The database contains the unique login ID of the user who watched it, the time when the user watched it, the IP address (unique online identifier) of the computer used to watch the video and the identifier for the video.
The database is stored on live servers at Google and equates to 12 terabytes of storage.
The judge also ruled that Google should divulge the details of every video that has ever been removed from YouTube, for whatever reason.
What is the motivation for this legal ruling?
Media giant Viacom is suing Google alleging massive copyright infringement. When it initiated legal action in March 2007 the firm said it had identified about 160,000 unauthorised clips of its programmes on YouTube, which had been viewed more than 1.5 billion times.
Viacom said it wanted the logging database to "compare the attractiveness of allegedly infringing video with that of non-infringing videos."
It wants to know if the most popular videos ever watched on YouTube infringe its copyright.
Who does this affect?
If you've ever watched a video on YouTube then the details of that viewing will be stored somewhere in that database.
This copyright case might be taking place in the US but it would appear the logging database makes no distinction between users in different countries.
Does that mean Viacom knows what I have watched online?
If Viacom wanted to, the firm would be able to see which particular YouTube user has watched which particular clips.
But that is not necessarily the same thing as knowing who you are and what you have watched.
Privacy advocates are concerned that a combination of a users' YouTube login ID, a computer IP address and a user's viewing habits might be enough to personally identify individuals.
The Electronic Frontier Foundation points out that many people pick login IDs that relate directly to them, including their name.
A computer's IP address is also not enough in every case to identify an individual user. IP addresses are typically allocated by a user's Internet Service Provider, and often change dynamically over time.
So Viacom would need to contact your ISP if it wanted to find out more information about the IP address.
But there is no suggestion that Viacom is going to do this, nor any suggestion that ISPs would comply with such a request unless backed by a court order.
Not has Viacom said it is interested in pursuing individual users of YouTube through the courts.
What does Google say about this?
Google said the log should not be handed over because of privacy concerns.
In its submission to the court it said: "Plaintiffs (Viacom) would likely be able to determine the viewing and video uploading habits of YouTube's users based on the user's login ID and the user's IP address.
But the court ruled these concerns were "speculative".
What else did the court rule?
Viacom had asked the court to order Google to handover the source code, the core programming that is at the heart of YouTube.
But the court rule that this was a "trade secret" and its disclosure threatened to damage Google's business.
What happens now?
Google is likely to challenge this order while the Electronic Frontier Foundation has called on Viacom to "back off this overbroad request".