Edward Snowden teaches how to be elusive to US National Security Agency

Edward Snowden's new declassified documents are devoted to network security systems that experts at the US National Security Agency find difficult to hack into.

A series of documents about various programs and codes that NSA hackers fail to break were published in Der Spiegel. The reports say how to protect oneself from the electronic surveillance of Western intelligence agencies to remain anonymous.

The NSA ranks assignments by levels of complexity - from one to five. The first stage is the most trivial one. Hacking such a system is not difficult at all. The fifth level is designated with the word "catastrophic" and actually means that the NSA is unable to either decipher the code or hack the program.

For example, reading personal messages on someone's Facebook account is on the second stage. The documents also tell of combinations of different techniques and applications that complicate the work of the NSA up to the fifth level. In addition to Internet traffic encoding browser Tor, the list includes VPN service that conceals location through the use of proxy servers, an analogue of anonymous chat CSpace that ensures a high degree of protection to any type of files, as well as voice call and text correspondence encoding ZPTR.

If all of the above technologies are used, the NSA will not be able to  keep tabs on users' online activities.