A senior intelligence official at NSA (National Security Agency) disclosed that Mr. Edward J. Snowden used very low cost web crawling tools to scraped data from NSA documents. Note that NSA have top grade security to protect against outside attacks and also responsible for protecting nation's sensitive military and intelligence computer systems from cyberattacks.
Snowden used low cost tools meant for web indexing & backup. Using very simple tool Snowden autoamted the process of documents downloads which otherwise would not have been possible by an outsider to access such huge volume of information. Snowden had access to NSA.
"Snowden had broader access to the NSA’s documents repository 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. " notes from NYT.