According to The Guardian, which published an article about the program on Wednesday, XKeyscore allows analysts to search -- without prior authorization -- through databases containing emails, online chats, and the browsing histories of millions of people. The newspaper reported that classified documents describing the program "shed light" on Snowden's assertion that, as an NSA contractor, he could "wiretap anyone, from you or your accountant, to a federal judge or even the president, if I had a personal email."
One training slide published by The Guardian claims that the program's ability to search HTTP activity by keyword covers "nearly everything a typical user does on the internet." According to the newspaper, the program allows analysts to search the metadata and content of emails and other internet activity of individuals being targeted. Searches can be conducted using name, telephone number, IP address, keywords, or language in which activity was conducted. The NSA documents claim that by 2008, 300 terrorists had been captured thanks to intelligence from XKeyscore.
XKeyscore collects so much information, it is impossible to store it all. From The Guardian:
The XKeyscore system is continuously collecting so much internet data that it can be stored only for short periods of time. Content remains on the system for only three to five days, while metadata is stored for 30 days. One document explains: "At some sites, the amount of data we receive per day (20+ terabytes) can only be stored for as little as 24 hours."
To solve this problem, the NSA has created a multi-tiered system that allows analysts to store "interesting" content in other databases, such as one named Pinwale which can store material for up to five years.
It is the databases of XKeyscore, one document shows, that now contain the greatest amount of communications data collected by the NSA.
It's important to point out, as The Guardian does, that the XKeyscore program provides the technological capability, but not the legal authority, to target U.S. persons for electronic surveillance without a warrant. In a statement, the NSA said XKeyscore is used as part of its legal intelligence work.
"XKeyscore is used as a part of NSA's lawful foreign signals intelligence collection system," the NSA said in a statement to The Guardian. "Allegations of widespread, unchecked analyst access to NSA collection data are simply not true. Access to XKeyscore, as well as all of NSA's analytic tools, is limited to only those personnel who require access for their assigned tasks ... In addition, there are multiple technical, manual and supervisory checks and balances within the system to prevent deliberate misuse from occurring."