Buried in the article is the key line: "the BBC has learned that Twitter was invited to join the Prism programme last year but rejected the approach from US au

Buried in the article is the key line: "the BBC has learned that Twitter was invited to join the Prism programme last year but rejected the approach from US authorities." So we now have a confirmation from a third party that at least one tech firm was approached about joining PRISM, and that joining wasn't legally compelled of them.