Guardian editors on Tuesday revealed why and how the newspaper destroyed computer hard drives containing copies of some of the secret files leaked by Edward Snowden.
The decision was taken after a threat of legal action by the government that could have stopped reporting on the extent of American and British government surveillance revealed by the documents.
It resulted in one of the stranger episodes in the history of digital-age journalism. On Saturday 20 July, in a deserted basement of the Guardian's King's Cross offices, a senior editor and a Guardian computer expert used angle grinders and other tools to pulverise the hard drives and memory chips on which the encrypted files had been stored.
As they worked they were watched by technicians from Government Communications Headquarters (GCHQ) who took notes and photographs, but who left empty-handed.