First, it can be used to browse the world wide web anonymously. It does this by routing traffic through many separate encrypted layers to hide the data identifiers that prove useful in police investigations.
Second, there are hidden sites on Tor that use the .onion domain suffix. These are effectively websites but, as they sit on Tor, are almost impervious to investigation.
to security forces Journalists and whistle-blowers use Tor to communicate with each other.
However, documents leaked by the whistle-blower Edward Snowden indicate the US authorities are concerned that terrorists and criminals are also using Tor to stay hidden.
The papers indicate that as a result the NSA has developed ways to track at least some of the people using the service.
http://www.bbc.co.uk/news/technology-26158012
