Snowden used low-cost tool to best NSA

Mr. Snowden had broad access to the N.S.A.’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 N.S.A.’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 N.S.A. headquarters at Fort Meade, Md., 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.