Edward Snowden: Gained access to high-classified documents using a web crawler.

Edward Snowden: Gained access to high-classified documents using a web crawler. Photo: Getty Images

Washington: United States intelligence officials say they have determined that Edward Snowden gained access to a huge trove of the country's most highly classified documents using inexpensive and widely available software to "scrape" the National Security Agency's networks, and he kept at it even after he was briefly challenged by agency officials.

Using "web crawler" software designed to search, index and back up a website, Mr Snowden "scraped data out of our systems" while he went about his day job, according to a senior intelligence official. "We do not believe this was an individual sitting at a machine and downloading this much material in sequence," the official said. The process, he said, was "quite automated".

The findings are striking because the NSA's mission includes protecting the nation's most sensitive military and intelligence computer systems from cyber attacks, especially the sophisticated attacks that emanate from Russia and China. Mr Snowden's "insider attack", by contrast, was hardly sophisticated and should have been easily detected, investigators found.

Moreover, Mr Snowden succeeded nearly three years after the WikiLeaks disclosures, in which military and State Department files, of far less sensitivity, were taken using similar techniques.

Mr Snowden had broad access to the NSA's complete files because he was working as a technology contractor for the agency in Hawaii, helping to manage the agency's computer systems in an outpost that focuses on China and North Korea.

A web crawler, also called a spider, automatically moves from website to website, following links embedded in each document, and can be programmed to copy everything in its path.

Mr Snowden appears to have set the parameters for the searches, including which subjects to look for and how deeply to follow links to documents and other data on the NSA's internal networks.

Among the materials prominent in the Snowden files are the agency's shared "wikis", databases to which intelligence analysts, operatives and others contributed their knowledge. Some of that material indicates that Mr Snowden "accessed" the documents. But experts say they may well have been downloaded not by him but by the program acting on his behalf.

Agency officials insist that if Mr Snowden had been working from NSA headquarters at Fort Meade, Maryland, which was equipped with monitors designed to detect when a huge volume of data was being accessed and downloaded, he almost certainly would have been caught. But because he worked at an agency outpost that had not yet been upgraded with modern security measures, his copying of data  raised few alarms.

"Some place had to be last" in getting the security upgrade, said one official familiar with Mr Snowden's activities. But he said Mr Snowden's actions had been "challenged a few times".

In at least one instance when he was questioned, Mr Snowden provided what were later described to investigators as legitimate-sounding explanations for his activities: As a systems administrator he was responsible for conducting routine network maintenance. That could include backing up the computer systems and moving information to local servers, investigators were told.

But from his first days working as a contractor inside the NSA's underground Oahu, Hawaii, facility for Dell, a computer maker, and then at a modern office building on the island for Booz Allen Hamilton, a technology consulting firm that sells and operates computer security services used by the government, Mr Snowden learnt something critical about the NSA's culture: While the organisation built enormously high electronic barriers to keep out foreign invaders, it had rudimentary protections against insiders.

Investigators have yet to answer the question of whether Mr Snowden happened into an ill-defended outpost of the NSA or sought a job there because he knew it had yet to install the security upgrades that might have stopped him.

"He was either very lucky or very strategic," one intelligence official said.

Through his lawyer at the American Civil Liberties Union, Mr Snowden did not specifically address the government's theory of how he obtained the files, saying in a statement: "It's ironic that officials are giving classified information to journalists in an effort to discredit me for giving classified information to journalists. The difference is that I did so to inform the public about the government's actions, and they're doing so to misinform the public about mine."

The NSA declined to comment on its investigation or the security changes it has made since the Snowden disclosures.

Officials, who did not want to be named, declined to say which web crawler Mr Snowden had used, or whether he had written some of the software himself. When inserted with Mr Snowden's passwords, the web crawler became especially powerful. Investigators determined he probably had also made use of the passwords of some colleagues or supervisors.

New York Times