Q. What is Prism?
It is a previously unknown programme run in the United States by the National Security Agency (NSA) to access data held by the world’s major internet companies, including Facebook, Google, Microsoft, Apple, Yahoo and Skype.
Q. What data can it obtain?
Detailed information about online activity, crucially including the contents of emails and live chat.
Q. How long has this been going on?
It is said to have been established in 2007 under changes to US surveillance laws passed by President George Bush and renewed last year by Barack Obama.
Q. How has this emerged?
Through a secret NSA presentation to staff which talks of “collection directly from the servers” of internet providers.
Q. How have the companies responded?
They deny knowledge of the programme despite the detail of the NSA presentation.
Q. How does this affect Britain?
As the primary sites of all the world’s major internet companies are in the United States, it means every communication by a UK national can in theory be read by NSA agents.
Q. Is this legal?
This is not clear, and privacy campaigners in Britain are investigating whether there are grounds for a legal challenge. Experts say the legislation covering the issue is sketchy.