It is known that for tracking the activities of Internet users (read correspondence by mail, browsing histories of visits to web pages in the browser and so on) NSA uses a program XKeyScore. To identify potential security threats to search by keywords. From the released source code XKeyScore became known that the filter on the NSA intercepted traffic turned out to be the rule where the adjoined keywords Tails (OS for anonymous Internet surfing), Tor anonymous network), and for some reason linuxjournal.com.
If someone from users simply looking at Linux Journal or mentions in the discussions of the Tor or Tails, it automatically can get under surveillance authorities.
Apparently, the NSA decided to control users Tails and Tor on third-party sites due to the fact that the final compromise the Tor network, which is used by human rights activists and dissidents around the world, does not work.