British officials said Friday that the trove of documents taken by National Security Agency leaker Edward J. Snowden, which it seized earlier this week at Heathrow airport, contains more than 58,000 "highly classified UK intelligence documents," which the government now assumes are in foreign hands.
Oliver Robbins, the deputy national security adviser for intelligence, security and resilience in the Cabinet Office, told a court in London that Mr. Snowden "indiscriminately appropriated material in bulk," including personal information that would allow British intelligence staff, some serving overseas, to be identified.
The 58,000 documents were among 60 gigabytes of encrypted data seized from David Miranda during a nine hour detention under special terrorism powers Sunday.
Mr. Miranda is the boyfriend of Glen Greenwald, the journalist for Britain's The Guardian newspaper who has been the conduit for most of Mr. Snowden's leaks. He was bringing the data to Mr. Greenwald at their home in Brazil when he was detained while changing planes in London.
Friday's court hearing was held to hear Mr. Miranda's lawyers' objections to the search of the material, but the judge ruled that the police could continue their efforts to decrypt the data.
The news, the first public comment by either the British or U.S. governments about the exact size of the trove that Mr. Snowden stole, suggests that his theft was of a much larger size than previously had been thought.
It is not known if the material recovered from Mr. Miranda represents the entirety of what Mr. Snowden took, which means his theft could even approach the scale of the cache that Bradley E. Manning passed to WikiLeaks — more than 750,000 classified documents — and at a much higher classification level.
Manning only had access to "secret" level documents, whereas those disclosed by Mr. Snowden have mostly been "top secret" or higher.
Britain has to assume the stolen data is now in the hands of foreign governments, since Mr. Snowden's prior travel to Hong Kong and Russia, Mr. Robbins told the court, according to the Daily Telegraph.
He added that among other material taken from Mr. Miranda was a piece of paper with a password to one of the encrypted files written on it.
"The claimant and his associates have demonstrated very poor judgment in their security arrangements with respect to the material," he said. This meant that it was a "real possibility" that "other, non-state actors," might also have accessed it.
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